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A PRACTICAL TREATISE 
ON FOUNDATIONS, 



EXPLAINING FULLY THE PRINCIPLES 
INVOLVED. 



DESCRIPTIONS OF ALL OF THE MOST RECENT STRUCTURES, AC- 
COMPANIED BY NUMEROUS DRAWINGS; ALSO AN ACCU- 
RATE RECORD OF THE BEARING RESISTANCES 
OF MATERIALS ASDETERMINED FROM THE 
LOADS OF ACTUAL STRUCTURES. 




W. M. PATTON, C.E., 

Formerly Professor of Engineering at the Virginia Military Institute ; 

Engineer in charge of the Mobile River, Ohio River, Susquehanna River, and Schuyl- 
kill River Bridges ; late Chief-Engineer of the Mobile and Birmingham 
Railway and of the Louisville, St. Louis, and Texas Railway. 



FIRST EDITION. "' ; & o?* f 



FIRST THOUSAND. 

NEW YORK: 

JOHN WILEY & SONS, 

53 East Tenth Street. 

1893. 






~'S 



P3 




Copyright, 1893, 

BY 

W. M. PATTON. 



, 



Robert Dbommokd^ 

Electrotyper, 

m and «6 Pearl St„ 

New York. 



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£ * * 



PREFACE. 



In a work on Foundations, theories and formulae are of 
little value ; therefore but little space is given to the discussion 
or criticism of either. The more common formulae are given 
without any attempt to explain the laws or premises upon 
which they are based ; a few examples are worked out in order 
to show the actual or relative values of the terms entering into 
them, and to compare the results with those used in practice. 
I do not do this either to ignore or underrate the value or im- 
portance of theoretical investigations ; if the formulae deduced 
in themselves do not have practical value, they incidentally- 
lead to comparisons with actual results, and induce the publica- 
tion of a large mass of more or less accurate records of observed 
facts. Theory and practice should go hand in hand ; but it 
is to be regretted that in many institutions claiming to be 
schools of engineering so great a preponderance in time and 
energy is given to the theoretical side of the question, even 
almost to the exclusion of practical instruction, whereby many 
erroneous ideas and principles are instilled into the minds 
of young engineers, to eradicate which years of labor, blun- 
dering, and mortification are required, causing loss and delays 
to their employers, loss and injustice to contractors by onerous 
and useless requirements and exactions, which could have been 
saved by a knowledge of a few facts and methods found in 



IV PREFACE, 

common and every-day practice ; theorists claiming that the 
"costs of labor, materials and construction, and also rules of 
practice " are of no value to the student of engineering, as 
these will be acquired after leaving college, and that " prin- 
ciples alone are necessary to be taught." 

Having been a professor for over six years, I have fully 
realized the need of suitable books, by which I could temper 
the almost painfully scientific, abstruse, and purely theoretical 
books that I was compelled to put into the hands of the 
student in engineering, which could only be partially supple- 
mented from a few years' prior experience in active practice, 
during which the full force of what I have stated above was 
fully realized. 

With the above experience and the experience derived from 
eighteen years of active practice, a very large portion of which 
was devoted to bridge construction in many parts of the 
United States, building on a great variety of soils, necessarily- 
requiring a great variety in the designs and methods of con- 
struction, I have undertaken to write the following pages. 
The descriptive portions of this volume have been to a large 
extent based upon my own experience, the facts of which are 
taken from records made at the time and still in my possession ;: 
they can therefore be relied upon as accurate. The drawings, 
with few exceptions, are taken from my own designs, and are 
accurate representations of the actual structures used ; in these 
my only aim was simplicity in design, convenience in construc- 
tion, combined with cheapness, strength, and suitableness for 
the purpose in view. Unusual sizes and shapes of the parts were 
studiously avoided, as only adding to the cost of material and 
construction without any compensating practical advantages. 
I have only given prominence to these, as I believed they can 
be fairly well taken as typical designs, and with a few modifica- 
tions in the details can be readily converted into the designs of 
other engineers for the same purposes. Full descriptions, how- 



PREFA CE. V 

ever, have been given of all of the latest and largest structures, 
which can be readily understood when taken in connection 
with the drawings given. I have collected from all available 
sources facts in connection with this all-important subject 
that have been published up to the present date, such as the 
actual loads and pressures on every variety of material, accu- 
rate descriptions of all designs and methods of construction, all 
useful knowledge of the qualities, properties, and strength of 
the materials used. Believing that the want of familiarity with 
the costs of materials and construction, the usual dimensions 
and forms of parts, and the quantities of materials required in 
the more common structures, as expressed in bills of material 
and records of actual and comparative costs of structures, is a 
most fruitful soures of waste of money in making contracts, as 
designing contractors, by magnifying the costs of materials and 
construction, and the difficulties and risks to be incurred, im- 
pose upon the credulity, ignorance and fears of engineers, there- 
by securing enormous profits on their works, for these reasons 
I have devoted more than the usual space to these matters. 
I have expressed opinions, made suggestions and (I hope) 
kindly criticisms, knowing full well that if they are erroneous 
or not justified by the facts presented they will be corrected, 
for which kindness I desire to express my thanks in ad- 
vance. No one need be misled by opinions, as the facts 
are present in full. I have endeavored in writing this volume 
to confine myself as closely as possible to matters pertain- 
ing to the subject of foundations, by which I mean those 
parts of structures resting on and directly supported by the 
materials of the earth, and these materials themselves in regard 
to their capacity to support the loads or pressures resting upon 
them. There has always been some confusion as to the mean- 
ing of the term Foundation : it is difficult, if not impossible, 
to separate that which supports a pressure from that which 
produces it. We must know the magnitude, the direction, and 



VI PREFA CE. 

the point of application of a force; and all three must be 
known. If the force is distributed, we must know the nature 
of the distribution, whether uniform, uniformly varying, or ir- 
regularly varying, so as to provide proper supports and resist- 
ances, with the requisite strength and at the required points. 
Except in so far as these considerations enter, I think that I 
have confined myself within the limits of the subject. To 
avoid confusion or too much repetition, I will always call the 
natural materials, of whatever nature, upon which the structure 
is founded or built, the Foundation-beds ; all else will be called 
Foundations or Substructures, these being the parts of the 
structure under the surface of the ground or water. Those 
portions above are only described or illustrated where it could 
not be avoided either for a clearer understanding or for sake of 
valuable comparisons. Where tables and other data have been 
taken from books, I have endeavored to give the authors the 
credit in the description. I am, however, largely indebted to 
the editors of the Engineering News, who kindly granted the 
free use of the columns of their valuable and wide-awake 
magazine. I am also under obligations to Mr. C. A. Brady. 
C.E. ; Mr. I. E. A. Rose, architect ; and Professor R. A. Marr r 
of the Virginia Military Institute, for valuable aid in prepar- 
ing the drawings. I have been greatly assisted in other ways 
by Col. E. W. Nichols, Prof, of Mathematics, Virginia Military 
Institute. 

The volume is divided into three parts ; it is further sub- 
divided into articles and paragraphs. The articles are numbered 
continuously throughout the volume, the paragraphs are only 
numbered continuously through each part. Par. I is at the 
beginning of each part. 

W. M. Patton, C.E. 

Lexington, Va., May, 1893. 



TABLE OF CONTENTS. 



PART FIRST. 

ARTICLE I. 



PAGE 

Foundation-beds:— Of rock, clay, sand, gravel, and silt— Rules for prepa- 
ration of— Bearing resistance of — Practical deductions— Tables of 
resistance to crushing of stone— Practical determination of bearing 
resistance of — Failure of structure mainly due to defective . . 1 

ARTICLE II. 

Foundations: — Means adopted in constructing — Of concrete— Composi- 
tion of concrete — Methods of mixing — Consistency of mortar in — 
Proportions in, of stone and mortar— Methods of mixing for the Ohio, 
Susquehanna, Schuylkill, and Tombigbee river bridges — Kinds of 
stone suitable — Broken bricks and shells in — Rules and principles in 
making— Proportions, mixing, etc., under Washington Monument — 
Absolute rules for proportion of quantities useful and practicable 
in certain cases — Impracticable when handling large quantities with 
limited time and money available 9 

ARTICLE III. 

Concrete: — Uses and advantages of — Under walls of houses, bridge piers 
and abutments, and retaining-w alls— Crushing strength of . . 20 

ARTICLE IV. 

Building Stones: — Granite, marble, limestone, slate, and sandstone— Prop- 
erties of, structural and chemical— Stratified and unstratified — Quarry 
indications as to quality — Siliceous, calcareous, argillaceous — Stones 
that harden by exposure, stones that disintegrate or deteriorate on 
exposure — Resistance to acid and atmospheric influences — Resistance 



viii TABLE OF CONTENTS. 



of, to heat— Capacity of absorbing water— Durability of, and suitable- 
ness for building purposes 23 

ARTICLE V. 

Quarrying: — Rules and principles— Drilling by hand and by machinery- 
Economical conditions of— Blasting with powder and dynamite, pre- 
cautions necessary to avoid injury to stones in — For face stones, for 
backing, rubble and concrete ........ 28 

ARTICLE VI. 

Stereotomy: — Only simple forms required for ordinary work — Useful for 
architectural and ornamental purposes, requiring complicated forms 
and shapes— Tools used — Methods used in cutting and dressing ordi- 
nary stones — Requirements as to beds and joints — Examination and 
inspection of stone — Chisel-drafts, pitch-lines — Models and templets — 
Necessary and unnecessary requirements . ... 34 

ARTICLE VII. 

Masonry: — Stones used in — Granite, marble, limestone, and sandstone — 
Classified — Dry stones, rough rubble, rubble in courses,block-in-course, 
ashlar — Stone suitable for — Relative dimensions of stone in — Facing 
and backing — Headers and stretchers — Dimensions and proportions — 
Bond in — Bed and side joints in — Ashlar, rubble, and concrete back- 
ing compared — Grouting walls of — Footing-courses, neat work, string- 
courses and coping, raising stones— Appearance of masonry on face 
no indication as to kind or quality of — Uses and advantages of chisel- 
drafts and-pitch-lines — Proper position, length, and other dimensions 
of headers „ .37 

ARTICLE VIII. 

String-courses and Coping: — Uses of —Projection of — Kind of masonry 
in — Position of — Shape of piers in plan — Square, circular, elliptic, and 
triangular ends— Templets for — How laid and constructed — For what 
purpose — Proportions of length and breadth of ends — Cutwater or 
starling proper 46 

ARTICLE IX. 

Ice and Wind Pressures: — Velocity and force of wind— Formula for — 
How estimated on piers and trusses — Pressure of ice — Force of wind — 
How estimated — Various theories and assumptions — Moment of over- 
turning forces on trusses and piers — Moment of resistance to over- 



TABLE OF CONTENTS. ix 



turning— Ice and drift gorges— Effect of, on structures — Dimensions 
of piers required determined by other conditions, and always suffi- 
cient to resist these external and unusual pressures — Examples given, 49 

ARTICLE X. 

Retaining- Walls:— Stability of masses of earth, frictional — Cohesion 
and adhesion destroyed by exposure— Angle of repose — Natural slope 
— Uses of — Resultant pressure on — Magnitude, direction, and point of 
application of resultant— Moment of overturning force — Moment of 
stability or resistance to overturning — Resistance to sliding or fric- 
tional stability — Formulae and practical rules for thickness of walls — 
Pressure of water or quicksand on, and thickness required— Con- 
struction of — Kind of masonry in — Face, backing, and footing courses 
— Position of centre of pressure or resistance with respect to centre of 
figure of base— Plan and Section— U, T, and wing abutments and 
walls 52 

ARTICLE XI. 

Retaining-Walls :— Formula? for stability — Rankine's, Trautwine's, 

Moseley's — Practical examples and rules 57 

ARTICLE XII. 

Arches: — Theory of— Mathematical and graphical methods— Depths of 
arch-ring at keystone and springing— Centres of pressure— Lines of 
pressure— Masonry in arch-ring— Abutments— Spandrel walls— Back- 
ing— Flat and pointed arches, manner of giving way — Backing to 
prevent failure— Stability of— Resistance to crushing, overturning, 
sliding— Definition of terms used— Full centre— Elliptical and seg- 
mental 64 

ARTICLE XIII. 

Skew Arches: — Definition of— String-course and ring-course joints— De- 
velopment of soffit — Usual construction of 72 

ARTICLE XIV. 

Arches:— Formulas for depth of keystone— Examples under— Lines of 
pressure 73 

ARTICLE XV. 

Brick: — Brick walls and piers — Brick-making— Uses and advantages of — 
English and Flemish bond— Construction and strength of— Durabil- 



X TABLE OF CONTENTS. 

PAGE 

ity of— Stability of— Failure of— Mortar, adhesion to— Use below 
ground or water not recommended unless cement mortar is used — 
Slate between courses— Importance of being kept wet— Thickness of 
walls— Compressed brick— Dimensions— Measurement of— Sewers- 
Pavements . 75 

ARTICLE XVI. 

Bbick Arches:— Usually built in rings— Headers should be used— Two 
methods of building— Thickness of joints at intrados and extrados— 
Slate in joints— Use and advantage of hoop-iron— Used in lining tun- 
nels—Thickness of lining— Uses of— Stability of— How estimated and 
paid for 82 

ARTICLE XVII. 

Akches: — Summary of theories and their practical applications— External 
forces — Assumptions made— Lines of pressure — Precautions necessary 
in constructing — Centres for arches 85 

ARTICLE XVIII. 

Box Culverts: — Uses, dimensions, and construction of — Kind of masonry 
in— Thickness of walls — Height — Covering stones — Precautions in 
filling over and around culverts and arches— Rules and principles of 
masonry construction 89 

ARTICLE XIX. 

Cements and Hydraulic Limes : — How and where obtained— Kind of 
stones — Percentage of lime, clay, or silica, etc. — Temperature required 
in burning — Mixture of different grades of stone — General properties 
and qualities — Portland, heavy slow-setting — Rosendales, light quick- 
setting — Hydraulic activity and energy — Set not well defined — How 
determined — Proportions sand, cement, and water — Tensile strength 
. of — Requirements of — Simple tests as to fineness, set, etc. — Slake 
slowly — Quick-lime obtained from pure carbonates, or those contain- 
ing small per cents of clay, silica, etc., and will not harden under 
water — Process of slaking— Mixing with water — Quantities of mortar 
obtained per barrel of cement and lime — Quantity required in mason- 
ry and concrete — Proportions of sand and water in mortars. . . 91 

ARTICLE XX. 

Mortar: — Definition of — Proportions of cement or lime, sand, and water — 
Proportions of, in masonry — Cement and lime mixed economical — 
Test of quick-lime and slaking of— Cement and quick-lime stones — 



TABLE OF CONTENTS. xi 



Chemical and mechanical composition of —Percentage of beneficial and 
injurious ingredients— Proper cements to be used— Tests of— Brands 
of— Tensile tests of briquettes— Hardening of lime and cement mor- 
tars—Deposited under water should have some set first, unless 
deposited in bags— Lime mortars not used under water— Pozzuolana— 
Definition and uses of— Freezing of mortars not considered injurious 
Experiments on— Salt in mortars— Pointing mortars. Also see Sup- 
plement ,96 

ARTICLE XXI. 

Sand:— Uses of, in mortar— Proportions— Qualities necessary— Sizes of 
grains — Tests for cleanness and sharpness— Salt-water sand — River 
and pit sand— Cleanness and sharpness of grain most important 
requirements 106 

ARTICLE XXn. 

Stability of Piers:— External pressures— Current, ice, drift, and wind- 
Expansion and contraction of ice— Effects on piers— Ice and drift 
gorges, and flow of— Destructive effects of— Tearing and crushing 
resistance of ice— Protection of piers, cutwaters, etc. . . ... 107 

ARTICLE XXIII. 

Water- way in Culverts:— Formula? for— Practical rules— Dimensions 
of, and how determined practically— Terra-cotta pipes— Iron pipes- 
Uses of culverts 113 

ARTICLE XXIV. 

Arch Culverts:— Dimensions and construction of— Thickness of abut- 
ments—Formulas for— Practical examples— Lengths of span— Plans 
and sections— Surcharged walls— Formula for— General remarks . 115 

ARTICLE XXV. 

Cost of Work :— Remarks on— Brick- walls and piers— Trestle work, 
framed and pile— Timber, masonry, caissons, cribs and coffer-dams- 
Conditions in contracts 120 

ARTICLE XXVI. 

Cost of Work:— Tables of— Cost of quarrying, cutting, laying, sand, 
masonry, brick-work, rubble, concrete, paving, brick, arch stones, 
cement, lime, etc 123 



x ii TABLE OF CONTENTS. 

ARTICLE XXVII. 

PAGE 

Dimensions, Quantities and Cost:— Examples— Ohio, Susquehanna, 
Schuylkill, Tonibigbee river bridges— Tables of quantities and costs 
—Cost of sinking caissons as usually estimated, also by cubic yard 
of displacement . 126 

ARTICLE XXVIII. 

Definitions and Tables: — Of parts of arches, piers, and retaining-walls, 
e t c . —Tables— Of resistance to crushing, tearing, cross-breaking— Of 
weights per cubic foot of materials— Of angles of repose— Of various 
materials— Of bearing resistance of soils— Uses of, and practical ex- 
amples * 136 



PART SECOND. 

ARTICLE XXIX. 

Timber Foundations:— Why used— Under walls of houses— How con- 
structed—Under New Orleans custom-house — Under towers— Unit 
pressures should be same under all parts— Piles often preferred in soft 
and silty soils— Cribs and grillages under piers— Construction of— 
Sinking of— Dangers of beds of sand and gravel— But often used- 
Example, Parkersburg bridge— Cribs sunk on rock— Precautions to be 

t a k en Cribs sunk on rock— Coffer-dams of earth, and dimensions 

of — Remarks on 147 

ARTICLE XXX. 

Coffer Dams of Timber:— Double walls with clay-puddle— How con- 
structed — Dimensions — Remarks on— Single wall coffer-dams, 
tongued and grooved— Construction of— With vertical timbers— 
With timbers and plank in horizontal layers— Crib coffer-dams 
—Construction uses and advantages— Puddle for— Pumps— Exca- 
vation Size of dam important — Bracing— Precautions for safety — 

Coffer-dams with inner cribs— Construction— Uses and advantages of 
—Examples— Preparation of foundation-beds 151 

ARTICLE XXXI. 

Open Caissons:— Construction of —Preparation of bed by dredging— By 
piles— For what depths useful and economical— Sides of, single wall 
coffer-dams, and removable— Bottom crib or grillage forms part of 



TABLE OF CONTENTS. Xlll 



permanent foundations — Generally simply resting on bed — Can be 
secured if necessary 162 

ARTICLE XXXII. 

Cushing Cylinder Piers:— Construction and uses— Piles actual supports 
— Cylinder casings for concrete — Use of concrete— Depths sunk — 
Manner of sinking— Piers wanting in stability — Are economical, and 
often used— Cylinders often sunk without piles— Require constant 
watching and large quantities of riprap— Examples— Tensas River 
bridge— Full description and dimensions— Sinking— Shell concrete 
used— Contract prices for, etc 164 

ARTICLE XXXIII. 

Sounding and Borings:— Importance of— Common neglect of — Making 
— Errors and waste resulting from neglect of — First method, driving 
solid rods, uncertain, unreliable, and unsatisfactory — Second method, 
sinking large terra-cotta or iron pipes more satisfactory, but more or 
less uncertain— Third method, sinking small iron pipes by water-jet 
and force-pump, rapid, economical, reliable, and satisfactory— Descrip- 
tion of processes in sand and gravel and silt. Also see Supplement . 166 

ARTICLE XXXIV. 
Timber Piers: — Construction and uses— Advantages and disadvantages . 170 

ARTICLE XXXV. 

Framed Trestles:— Construction and uses— Designs and dimension of 
parts 172 

ARTICLE XXXVI. 

Properties of Timber: — Kinds commonly used — Pine, oak, cypress — 
Effects of bleeding or turpentining pine-trees . . . . 177 

ARTICLE XXXVII. 

Durability op Timber:— Defects of, cracks, shakes, crippling, dotiness, 
sponginess, decay, and rot where developed in frame structures 
— Examinations for — Repairs and renewals — General remarks . . 180 

ARTICLE XXXVIII. 

Preservation of Timber: — Character of defects— Effect of, on timber — 
Natural seasoning— Protection of bridge trusses — Artificial seasoning — 



xiv TABLE OF CONTENTS, 



Preservation by solutions of metallic salts, creosoting, vulcanizing— 
Durability as affected by time of cutting down and by age of trees— 
Constantly immersed in water, favorable for durability— Asphalt and 
other paints— Discussions and remarks. Also see Supplement . . 182 

ARTICLE XXXIX. 

Framed Trestles:— Two types not often used, but good designs- 
Joints, weak points in . . . 187 

ARTICLE XL. 

Joints and Fastenings: — Mortise-and-tenon— Disadvantage of— Square 
abutting joints with iron straps— Advantages of — Dovetail joints 
— Strut and tie — Longitudinal bracing— Fish and scarf joints — 
Uses and designs — Actual and relative strength of joints — Formulae 
and examples of relative resistance to crushing, tearing, and shearing — 
Strength of connections should equal strength of main parts — Weak- 
est part determines strength of entire structure — Joints in king and 
queen trusses — Rules and principles to be followed in all joints and 
fastenings — Joints for lengthening — Ties, struts, ties and struts, and 
beams 188 

ARTICLE XLI. 

Trestle Foundations: — Mud-sills — Masonry pedestals — Piles— Advan- 
tages and disadvantages of — Framed trestles divided into four classes 
— Comparative strength and economy of construction — Kind of stresses 
on main members— How connected to resist — Formulae for and 
examples of relative and actual strength and dimensions — Posts, caps, 
sills, stringers, struts, and braces — Explanation and use of formulae — 
Tables of resistance to crushing, tearing and cross-breaking — Ulti- 
mate and working stresses, factors-of -safety — Formula for long columns 
— Bill of timber and iron for four story trestle 196 

ARTICLE XLII. 

Timber Piles: — Uses of — Long and short— Kind of timber used, and com- 
parative value — Preparing piles for driving — Squaring butt — Pointing 
end — Square ends preferred in driving — Method of driving— Precau- 
tions to prevent splitting — Excessive brooming — Bands and shoes of 
iron — Remarks on driving — Great damage to piles in driving — Useless 
hammering on piles — Value of formulae discussed — Reliance mainly 
on experiment and experience — Experiments on bearing power of 
piles (also see Supplement) — Practical conclusions — Peculiarities in 



TABLE OF CONTENTS. XV 

PAGE 

driving in different soils— Remarks — Usual formulae and examples 
under them — Rankine's, Trautwine's, banders' 207 

ARTICLE XL1II. 

Timber Piles: — Engineering News formula — Latest aud doubtless the 
best — No formula considered of practical value depending on weight 
of hammer, fall and penetration — Formula suggested for bearing re- 
sistance based on bearing resistance of soil and factional resistance on 
exposed surface of pile — Only formula applicable to piles sunk by 
water- jet or otherwise forced in ground without blows of hammer — 
Examples under — Several forms of pile-driver used — Description and 
discussion — Hand, horse, and steam-power. Also see Supplement . 219 

ARTICLE XLIV. 

Piles: — Purposes for which driven — Long aud short — Sand piles — Under 
houses, piers, wharves, and dikes — Pile-trestles extensively used — Dis- 
cussions of three and four pile bents, with vertical aud batter piles — 
Designs of floors or decks — Economical considerations— Piles in differ- 
ent kinds of materials — Piles on rock bottoms — Cribs often substi- 
tuted for — Construction and sinking of cribs 226 

ARTICLE XLV. 

Comparative Estimate op Costs Framed and Pile Trestles: — Tres- 
tles mainly temporary expedients, iutended to be replaced by iron, 
masonry, or earthen embankments — Relative cost and quantities in 
framed and pile trestles — Timber and iron — Tables of iron, with drift- 
bolts —Straps — Mortise-and-tenons — Importance of — Discussion of 
economic length of span for low and high trestles— Calculations and 
comparisons — Manner of estimating and paying for trestles — Useless 
requirements — Local customs important to observe — Cutting piles off 
under water — Divers — Cross-cut aud circular saws—Structures resting 
on piles— How secured — Proper alignment of piles — Remarks . . 235 

ARTICLE XL VI. 

Embankment op Earth on Swamps: — Supporting power of swamp crust 
— Depth sunk in underlying soft silt — Logs and plank used to support 
— Objections to these methods — General remarks on earth-work — Ma- 
terials for — Form and dimensions of embankments— Grades — Settle- 
ment of banks — Borrow-pits — Side drains — Caving in of slopes — 
Prevention of — Ballast for — Cross-ties— Pine, oak, and lignum vitae — 
Hewn and sawn cross-ties — Costs of — Recent methods of embanking, 



Xvi TABLE OF CONTENTS. 



as compared with older — Swampy material unfit for embankments — 
Formula for bearing power of soft materials, to be used with caution 
— Soft stratum underlying a firmer one, and vice versa . . . 251 



PART THIRD. 

ARTICLE XL VII. 

Deep and Difficult Foundations:— Open crib and pneumatic caisson 
methods— Crib-methods — Discussion and examples — General designs 
for timber and iron constructions— Methods of sinking— Examples — 
Poughkeepsie, Hawkesbury, Morgan City bridges — Discussion — 
Advantages and disadvantages— Difficulties — Costs and quantities . 262 

ARTICLE XLVIII. 

Pneumatic Caissons: — Air an essential element — Plenum and vacuum 
methods — Uses of — Principles and practical applications — Working 
chambers — Air-locks — Uses and position of— Shafts, pipes, etc. — 
Safety precautions — Number of men required — Effect of compressed 
air on men— Selection of men — Precautions for their comfort and 
safety — Paralysis and death in caisson work — Means of preventing, 
suggested — Signals — Immediate effect of reducing air pressure — Ma- 
chinery 274 

ARTICLE XLIX. 

Pneumatic Caissons: — General designs and construction — Examples — 
New York and Brooklyn — Missisippi at St. Louis and Memphis — 
Diamond Shoals Light-house— Ohio River at Cairo— Susquehanna, 
Schuylkill, Tombigbee caissons — Quantities and cost — Full discussion 
of each structure — Cribs and coffer-dams on caissons — Full details of 
construction, sinking, and costs — Accidents, precautions against — 
Cribs not absolutely necessary — Masonry may be commenced on roof 
of caisson — Coffer-dams should always be provided — Designs and 
construction of cribs and coffer-dams — Uses and advantages. . . 283 

ARTICLE L. 

Caisson Sinking: — Sand and mud pumps, and blowing-out process for 
excavating material — Precautions necessary in removing material 
from under cutting edges— Some difficult cases — Excavating below 
cutting edge in sand, clay, and silt — Filling cribs and working cham- 
bers with concrete — Precautions in passing concrete through supply 



TABLE OF CONTENTS. xvii 



PAGE 

shafts— Mixing concrete for— Considerations requiring caissons — 
Causes of some accidents— Difficulties and costs — Lessons to be learned 
— Discussions of — Frictional resistances on outside surfaces . . 302 

ARTICLE LI. 

Combined Crib and Caisson:— Design, construction, and uses— First as a 
caisson, second as a crib, third as combined crib and caisson — Con- 
sists of an ordinary caisson or open crib, provided with one or more 
removable roofs, by means of which it can be sunk to any desired 
depth as a pneumatic caisson— One or more roofs removed, and sink- 
ing continued if desired by open crib process — Use in small depths- 
Requiring only one or, better, two roofs— After sinking, and sealing up 
working chamber, roof removed — Concreting is completed in open air 
or under moderate pressure— Better, more rapid, and satisfactory work 
— Substituted for ordinary coffer-dams— Construction and sinking 
described— Safety and comfort of men provided for — Economy, cer- 
tainty, and rapidity in sinking— "When sunk to depths of 100 ft. by 
pneumatic process, piles can be introduced and driven, or sinking 
continued by open crib method to any greater depth— Average lift of 
dredged material decreased, and also cost, as compared with open crib 
process— Constructed of timber or iron, or both combined, in any of 
designs already given— General remarks on— Unnecessarily sized and 
shaped parts— Cost and increased difficulties in construction of caissons 
— Poor designs, etc 3U 

ARTICLE LII. 

All-Iron Piers:— Of wrought-iron columns resting on masonry piers 
or pedestals— Description— Advantages, dangers, risks— Precautions 
necessary— Screw-pile piers— Full description and discussion of 
designs— Methods of construction— Sinking piles— Both by turning 
and by water-jet— Advantages and disadvantages . . . .321 

ARTICLE LIII. 

Location of Piers:— By triangulation and direct measurements with 
tapes or wires— Instruments required— Base lines— Remarks on loca- 
ting bridge sites— Reasons controlling same — Examples of some of 
the longest spans and highest piers 325 

ARTICLE LIV. 

Poetsch Freezing Process:— Details and discussions— Description of 
method— Considered as the best method of sinking through quicksand. 33Q 



xviii TABLE OF CONTENTS. 

ARTICLE LV. 

PAGE 

Quicksand defined — The most difficult material to deal with in putting 
in foundations — Old methods of sinking through — Freezing process 
applicable — A more recent method — by injecting cement grout under 
pressure through pipes into the quicksand, which on setting converts 
quicksand into an artificial stone — Discussion and description of this 
last method— Sinking hollow cylinders of brick, concrete, or iron 
through — Methods and examples , 336 

ARTICLE LVI. 

Foundations for High Buildings: — Unit weights allowed on sand, clay, 
and silt — Usual methods on sand and clay — Sinking through soft 
materials, by shafts, cylinders, etc., to rock, or by driving piles — The 
three methods compared and discussed — Economy controlling factor — 
Masonry on concrete — Iron rails or beams imbedded in concrete — 
Formulae for projection of successive courses — Timber platforms or 
grillages on natural material or beds of concrete — Some examples of 
actual loads — East River Bridge — Capitol building at Albany— Bridge 
at London — Washington Monument — Tay Bridge, Scotland — Hudson 
River Tunnel — Eiffel Tower, Paris— City Hall, Kansas City — Audito- 
rium Building, Chicago — Bearing resistance under piers and frictional 
resistance on surface of caissons as given usually uncertain and 
unreliable— Examples of— Cairo, Bismarck, Susquehanna river 
bridges — Methods of determination different — Importance of accurate 
determinations and full records — Effects of compressed air in caissons 
and escaping under cutting edge reducing frictional resistance — Resist- 
ance to pulling piles less than that to force them down, with reasons 
for same — Examples of frictional resistances — Records few and uncer- 
tain 343 

ARTICLE LVII. 

High Buildings: — General discussions of methods offered to builders — 
First, direct building on ordinary soils— second, timber platforms, 
grillages, or cribs on soils— Third, iron or timber beams imbedded 
in concrete — Fourth, piles driven to rock, or supported by direct re- 
sistance at point and by frictional resistance on surfaces in contact 
with soil — Fifth, well sinking, with timber-lined shafts, brick, con- 
crete, or iron lined cylinders, or by open cribs or pneumatic caissons — 
Remarks on and general discussion of methods — Kansas City Hall — 
Manhattan Building, New York— Masonry-lined cylinders— Madras 
Railway, Iudia— Kentucky and Indiana Bridge piers, Ohio River- 
Iron cylinders, brick and concrete lined — Hollow spaces filled with con- 
crete after sinking— Methods and costs of construction. Also see Sup- 
plement 359 



TABLE OF CONTENTS. XIX 

SUPPLEMENT. 

PAGE 

Hawarden Bridge — Large cylinders, partly of iron and partly of brick — 
Filled with concrete — Construction and methods of sinking — Piles 
sunk by water- jet — Description and cost 369 

Foundations and floors for the buildings of the World's Columbian Ex- 
position — Lay and character of underlying strata — Load allowed per 
square foot on sand, amount of settling — Platforms and piles, when 
used — Pneumatic work under pressure greater than ever used hereto- 
fore — Tunnel under river — Progress, depths, etc. — Paralysis and 
deaths — Compare favorably with preceding pneumatic work . . 372 

Importance of borings and soundings, as illustrated by failure and neces- 
sary removal of large pier constructed in Coosa River, at Gadsden, 
Ala. — Causes, consequent cost, etc 373 

Bearing power of piles — Discussion of formula?, with numerous records 
of actual loads on piles and calculated safe loads for same by formula 
— Weights of hammers — Falls — Penetration in sand, gravel, clay, and 
silt — Numbers — Lengths and general conditions of driving . . 376 

Preservation of timber by vulcanizing process — Description of method, 
pressure, and temperature required — Chemical changes and reactions 
in fluid constituents of timber — Resulting product — Experiments 
showing increased strength, stiffness, and durability — Tensile strength 
of cements — Tests made from 1 day to 4 years — Natural Portland 
cement 386 



A PRACTICAL TREATISE ON 
FOUNDATIONS. 



PART FIRST. 



Article I. 

FOUNDATION-BED. 

1. NOTWITHSTANDING the almost infinite variety of material 
upon which we have to build and do build, there are certain 
general principles that should be followed, and which are 
applicable in all cases. 

2. First. The surface of the foundation-bed, excepting 
where piles are used, should be perpendicular to the direction 
of the resultant pressure, i.e., horizontal in case of ordinary 
bridge piers, walls of houses, and in general, in all cases where 
the resultant pressure is vertical ; and in fact in cases where the 
resultant pressure is inclined to the vertical — as in case of re- 
taining-walls, a horizontal foundation-bed will usually prove 
to be safe. This does not mean that on solid rock the founda- 
tion-bed must be cut over its entire surface to one horizontal 
surface, or even cut into a series of horizontal surfaces resem- 
bling steps, — this costs a great deal of time and money, — but 
that the surface of the foundation shall be so roughened as to 



A PRACTICAL TREATISE ON FOUNDATIONS. 



prevent the possibility of the substructure slipping on the 
foundation-bed. Illustrated by the following diagrams : s 

Fig. i. — Longitudinal Section of Foundation-bed on Rock. 




WWM 



**# 




^ 



*** 

Fig. 2.— Transverse Section of Foundation-bed on Rock. 

This is especially applicable to a foundation-bed of rock. 
In all other materials a uniform horizontal surface or a series 
of steps will be found both convenient and economical. And 
in fact in rock a series of blast over the surface, making a 
number of irregular depressions, will satisfy all conditions of 
safety. 

3. Second. An excavation must be made for a certain 
depth, depending mainly upon the depth to which alternate 
freezing and thawing takes place ; this depth — say from (2) two 
to (6) six feet — depending upon the climate and latitude, but 
may be limited in rock to removing loose and disintegrated 
portions. 

4. Third. As far as possible, surface water should be ex- 
cluded from the foundation-bed, and all possibility of running 
water should be absolutely excluded. This is accomplished 
by surface drains, and where necessary by subsoil drains. 

The principles above stated are applicable to rock, clay, 
sand, gravel, and various combinations of the three latter. 

5. Fourth. Uniformity of material in the foundation-bed 
is absolutely necessary. It is almost certain that any kind of 
material, except rock, will settle more or less under pressure, 
and will settle irregularly, consequently the structure will 
inevitably crack somewhere. Build wholly on one or other of 
the materials mentioned. 

6. Fifth. The weight of the structure should be as uniform 
as possible, and the structure should be built on all sides as 



FO UN DA TION-BED. 3 

nearly of the same height as possible. If heavy towers, such 
as the spires of churches, and they are bonded at all to the body 
of the building, special provisions (hereafter described) should 
be made so as to make the unit pressure (pressure per square 
foot of foundation-bed) the same as under any other part 
of the structure. 

7. The above principles being followed, safety against slip- 
ping if fully provided, and partly against settling. But an- 
other important element is the unit weight or pressure per 
square foot of structure upon the foundation-bed. Our knowl- 
edge as regards the capacity of bearing weight is meagre, and 
such as we have is conflicting and uncertain. The test of a 
cubical block of stone 2 in. X 2 in. X 2 in. of 4 sq. in. of sur- 
face, with cushions of pine, lead, or other substance, under 
pressure, can scarcely be considered as determining the crush- 
ing resistance of immense volumes of the same material in 
quarries or when built into massive structures, as valuable as 
it may be in other respects. But even the strength thus 
attained is sufficient to carry any load liable to occur in prac- 
tice. 

8. To illustrate: the most reliable authorities give the resist- 
ance to crushing of weak sandstone 3000 lbs. per square inch ; 
a granite pier 180 ft. high, carrying one half of two spans of 
525 ft. length and a rolling load of 3000 lbs. per lineal foot, 
gives a resultant weight of only 150 lbs. per square inch, giving 
a factor-of-safety of 20. Therefore we may conclude that 
almost any structure that we are likely to build can be safely 
constructed on the three types of rock commonly met with — 
granite, limestone, sandstone. 

9. Some authorities class clay, sand, sand and gravel to- 
gether, and state that 3000 lbs. per square foot of foundation-bed 
is the greatest intensity of pressure admissible. The writer, 
however, gives to clay the precedence, for the following rea- 
sons : Clay is more compact ; along with its tendency to retain 
water it has an equal power of excluding water; if settlement 
takes place it is apt to be uniform under same pressure, and 
consequently is less liable to cause damage to structwre above ; 



4 A PRACTICAL TREATISE ON FOUNDATIONS. 

it does not scour, and the weight on such material has a ten- 
dency to aid in keeping water out of that space over which 
weight is distributed. Water can be more easily kept from the 
foundation-bed either by surface or subsoil drains. The above 
authorities do not state the exact quality of material alluded 
to, as clay may vary from a soft, pliable clay, through loam, a 
mechanical mixture of clay and sand or what might be called 
"brick clay," and marl, a mechanical mixture of carbonate of 
lime and clay, together with certain silicates and protoxide of 
iron, then culminating in what may be called an indurated clay. 
10. If the low unit pressure, 3000 lbs., is the limit of safety, 
but relatively small structures should be built upon it without 
taking unusual precaution to distribute the pressure over a 
large area or by compacting the material by the use of piles. 
Taking the weight of a brick wall at 120 lbs. per cubic foot, the 
material above mentioned would only bear a column of ma- 
sonry 25 ft. high and 1 sq. ft. base; but this weight or pressure 
can be easily distributed over two, three, or more square feet of 
foundation-bed. So for any ordinary structure the above limit 
of resistance need not be exceeded, and in view of the fact that 
so many structures do settle and often cause dangerous cracks, 
it is unwise to take any risk. The writer built a bridge across 
the Ohio River at Point Pleasant, W. Va., on what he has 
classed an indurated clay — evidently a clay containing car- 
bonate of lime. It could be worked into a paste with water. 
Frequently the pit would be flooded. After pumping out the 
water a thin layer of slush or paste would be found. When 
this was scraped off, to the depth of an inch, rarely more, the 
surface was as dry and as hard as before. The largest pier was 
about 100 ft. high, carrying one span of 400 ft. and another of 
200 ft., built of sandstone, producing approximately a pressure 
of 5000 lbs. per square foot of foundation-bed, assuming sand- 
stone at 150 lbs. per cubic foot and spread doubling area of 
base. These, then, can be taken as the safe limits for a clay 
foundation. Some clays have seams in them, generally sloping 
at a greater or less angle to the vertical : these, if extensive, are 
dangerous, as the water will percolate along them, causing a 



FOUNDATION-BED. 5 

dangerous tendency to slide. In these cases the water must be 
excluded or the depth cut into material greatly increased. 

11. Building on sand was pronounced dangerous in the 
Bible, and has been so considered ever since ; but circum- 
stances often compel us to build on this tempting material, 
and as it may be said take the chances. Sand, when confined, is 
considered practically incompressible within the limit of actual 
crushing the grains of sand into impalpable powder. Sand will 
hold your structures if you can hold the sand. But here is the 
difficulty: it is porous, and unless confined in walls of rock or 
clay there is always danger of the water passing through, 
scouring out the material, and undermining the foundation, 
this process being greatly aided by the weight of the struc- 
ture, and sometimes forming with water quicksand, which is 
almost as unstable as water itself. Therefore in building on 
sand under no circumstances exceed the limit of weight of 5000 
lbs. per square foot of foundation-bed, and in addition be sure 
of excluding the water, or in exposed situations drive piles. 
More on this point hereafter. Beds of gravel and bowlders 
especially can certainly be relied upon, to at least the superior 
limit for clay of- 5000 lbs. per square foot of bearing surface. 
Two of the high piers of the Susquehanna River bridge, 
B. & O. R. R. at Havre de Grace were built on bowlders 
large and small, but at a great depth below the bed of the 
river, in which the frictions on the sides supports much of the 
weight. 

12. The remaining material of silt or slush, such as we 
find in all the swamps, especially in the Southern States, can 
scarcely be made safe without the use of piles, for very heavy 
structures; but by the liberal use of broken stone, or even in 
some cases of sand or gravel, a reasonably stable foundation- 
bed may be artificially constructed, which will be fully 
explained further on. The above sets forth fully the actual 
and relative merits of foundation-beds generally met with in 
actual practice. All of these matters will be incidentally 
alluded to when we come to discuss foundations, which is the 
next division of the subject to be treated. 



6 A PRACTICAL TREATISE ON FOUNDATIONS. 

13. A combination of these materials is frequently met 
with, the bearing-power of which may practically be taken the 
same as above ; but frequently these combinations take the 
form of what is called hardpan, or cemented sand and gravel, 
that would certainly justify a higher classification, and would 
not be inferior to the ordinary kinds of rock. There is no mis- 
taking this material when met with, and it can be relied upon 
to bear the weight safely of any ordinary structure. In many 
of the Southern States there is an earthy substance which 
may be called a marl, easily cut into blocks, difficult to exca- 
vate, requiring blasting sometimes, and capable of bearing 
heavy loads, but disintegrating rapidly when exposed to the 
air, and consequently unfit for building purposes. The writer 
founded several piers on this material, carrying long spans 275 
ft. in length ; the piers were of brick and the pneumatic cais- 
son used, passing through sand and silt before reaching it. 
This material almost disintegrated by slacking when exposed ; 
it effervesced freely with acids. 

14. The practical deduction from the above, then, may be 
stated as follows : 

1st. That it is in general perfectly safe to build, on any 
material that can be called rock, any structure likely to be 
required. 

2d. Bowlders and gravel can also be considered perfectly 
reliable for any ordinary structure under any ordinary condi- 
tions. Scour alone should be guarded against, which, however, 
is not probable. 

3d. Sand is safe to bear a load of any amount, provided it 
is confined ; but great precaution must be taken to confine it,, 
and also keep water, especially running water, from it. 

4th. Clay, when compact and dry, will likewise carry very 
large loads. Water should be kept from it both under and 
around the structure, as it may give way if it gets in the con- 
dition of paste by bulging up around the structure. 

5th. In the last three cases the base of the structure should 
be so spread out as to keep the pressure per square foot of 
base within the safe limit, and the depth below the surface 



FOUNDATION-BED. J 

must be below the action of frost, which varies from 2 ft. to 
6 ft.; and in soft kinds of material the deeper the better. 

15. A thick, hard, or compact strata overlying a much softer 
one, even silt or quicksand, will often carry a considerable load, 
the hard strata as it were floating on the softer. It is some- 
times better not to break through it, as it has the effect of 
spreading the base and distributing the pressure over a large 
area. Good judgment is here required, and some risk must be 
run. This principle is followed when planks or logs are spread 
out on the soft material, and the structure built on the logs, 
the logs forming a broad bearing surface. Mr. Rankine states 
that Chat Moss was crossed by the use of dry peat and hurdles 
or fascines in layers forming a raft, which carried a railway on 
it. It would seem safer and more satisfactory in such cases to 
drive piles. 

16. The following figures give the actual bearing-power of 
some of the above materials. 

Mr. Rankine says, page 361, "Civil Engineering:" 

Granite 12,861 lbs. per square inch. 

Sandstone 9,842 " " 

Soft sandstone. .. 3,000 to 3,500 " " " " 

Strong limestone 8,528 " " " " 

Weak limestone 3»05o " " " " 

Clay, sand, and gravel.. 17 to 23 " " " " 
Brick 1,100 " " " " 

And gives the actual pressure on some existing foundations 
as only about 140 lbs. to the square inch, giving an actual 
factor-of-safety of about 22, whereas factor-of-safety from 8 
to 10 is considered ample. These are probable average 
values. 

17. Mr. Baker, in his treatise on Masonry Construction, 
page 10, gives the following as the crushing strength of stone : 

Granite from 12,000 to 21,000 lbs. per sq. in. — 860 to 1,510 tons per sq. ft. 
Marble from 8,000 to 20,000 lbs. per sq. in. =. 580 to 1,440 tons per sq. ft. 
Limestone from 7,000 to 20,000 lbs. per sq. in. = 500 to 1,440 tons per sq. ft. 



8 A PRACTICAL TREATISE ON FOUNDATIONS. 

Sandstone from 5,000 to 15,000 lbs. per sq. in. = 360 to 1,080 tons per sq. ft. 

Brick from 674 to 13,085 lbs. per sq. in. = 48 to 936 tons per sq. ft. 

\\ Clay from 28 to 84 lbs. per sq. in. = 2 to 6 tons per sq. ft. 

Gravel from 112 to 1,401 lbs. per sq. in. = 8 to 10 tons per sq. ft. 

The above doubtless gives the results of the latest experi- 
ments. There are special cases when the loads actually borne 
are greater than the above ; but we can safely conclude that 
good ordinary clay will carry safely two tons per square foot ; 
sand, from 3 to 4 tons to the square foot, provided it can be 
kept entirely free from water. 

18. In cases of doubt and the absence of precedent, when 
unusually heavy loads are to be carried, and especially when 
the weight of the structure is not uniformly distributed, as in 
case of high towers and spires, tests should be made by actual 
weights placed on a unit of area, which can be done at the cost 
of but little time and money ; and as the means are always in 
reach to make the foundation safe, it is certainly inexcusable, 
to say the least of it, to blunder along and take the chances of 
the structure falling, involving great loss of property, if not of 
life, and only to avoid expending a few dollars. 

19. When structures fail, it may in general be said that it 
is impossible to determine the cause, though in general it is 
easy to get numberless opinions of so-called experts, and with 
these the public and juries are satisfied ; but in a large majority 
of cases it can be traced to that part of the structure under 
ground or under water, and ultimately due to the failure of the 
foundation-bed : for even if the part of the structure under 
ground is defective in some of its parts, it throws an excessive 
weight on some part of the foundation-bed. The failure, from 
high winds, from thrusts of roof or floors, or from floods, drift, 
and ice, is generally indicated by the manner of the falling ; 
and though this may evidently be the direct cause of failure, 
yet, indirectly the foundation-bed is at fault, as these cause 
undue pressure on some parts or scour out the foundation- 
beds and undermine the structure, as other conditions and re- 
quirements always require such weights and sizes of structures 
as will resist the outside forces. The dimensions of bridge 



FOUNDATIONS. 9 

piers are regulated generally by the dimensions at the top re- 
quired as a rest for the bridge structure, and are greater than 
that necessary to withstand the effects of these external forces. 
Be sure of your foundation and foundation-beds, and except in 
extreme cases the upper part of the structure will take care of 
itself. 



Article II. 

FOUNDATIONS, 

20. THIS division of the subject includes that part of the 
substructure reaching from the foundation-bed to the surface 
of the ground or the surface of the water, and necessarily in- 
cludes the various means of reaching the foundation-bed, such 
as ordinary excavations on land, driving piles on land or in 
water, screw-pile foundations, Cushing cylinders, coffer-dams, 
pneumatic cylinders, pneumatic caissons, open caissons, pierre- 
perdue foundations on land or in water, sand foundations in 
swamps, concrete foundations, rubble-stone foundations, etc. 

21. Each of these divisions will be treated more or less 
elaborately, but purely from a practical standpoint and as con- 
cisely as the importance of the subject may demand, consist- 
ently with that amount of detail as may be necessary to a clear 
understanding of the matter. These will also be accompanied 
by drawings giving sufficient details to be of actual and practi- 
cal use. Many books mystify with useless formulae, and give 
just enough practical information and details as to leave you 
in doubt whether you know anything at all, as it is generally 
admitted that in many cases the formulae have no practical 
value. This the writer hopes to avoid, and at the same time 
not to extend the limits of this subject too far. 

CONCRETE. 

22. As concrete is used so extensively, and in combination 
with almost all kinds of foundations, we will commence with 

this material. 



IO A PRACTICAL TREATISE OX FOUNDATIONS. 

Concrete is composed of broken stone or gravel or both r 
sand, cement, and water, mixed under certain circumstances in 
absolutely definite proportions, so as to obtain a conglomera- 
tion which experiments, conducted principally by Government 
engineers, have shown ultimately to produce the best possible 
results ; and doubtless in all works this practice would be fol- 
lowed, if in works paid for by private individuals or companies,, 
we had the money and time at our disposal. But in works of 
this class we must aim to attain as near perfection as practica- 
ble, but be satisfied with what is good enough for the purpose: 
in view, with the least possible cost in time and money, con- 
sistent with securing a permanent, strong, safe, and durable 
structure. We will first, however, explain the process of mak- 
ing concrete in accordance with the requirements of the Gov- 
ernment engineers. 

23. Gen. Q. A. Gillmore's treatise on Limes, Hydraulic 
Cements, and Mortars is assumed to be high authority, — a book 
which contains valuable and interesting information. On page 
226, paragraph 450, we find : " The concrete was prepared by 
first spreading out the gravel on a platform of rough boards, 
in a layer from eight to twelve inches thick, the smaller peb- 
bles at the bottom and the larger on top, and afterwards 
spreading the mortar over it as uniformly as possible. The 
materials were then mixed by four men, two with shovels and 
two with hoes ; the former facing each other and always 
working from the outside to the centre, then stepping back 
and recommencing in the same way, and thus continuing the 
operation until the whole mass was turned. The men with 
hoes worked each in conjunction with a shoveller, and were 
required to rub well into the mortar each shovelful as it was 
turned and spread, or rather scattered on the platform by a 
jerking motion. The heap was turned over a second time in 
the same way, but in the opposite direction ; and the ingredi- 
ents were thus thoroughly incorporated, the surface of every 
pebble being well covered with mortar. Two turnings usually 
sufficed to make the mixture complete, and the resulting mass 
of concrete was ready for transportation to the foundation." 



FO UNDA TIONS. I r 

There is but little comment to make; the method for hand- 
mixing can be safely recommended. The writer has mixed large 
quantities in practically the same manner, with these modi- 
fications : Firstly, the broken stone or gravel was not screened 
so as to separate the larger from the smaller sizes, and place 
the smaller pebbles at the bottom and the larger on top. The 
broken stone or gravel, within special limits as to the large 
size, the limit being such as would pass through a 2^-inch ring, 
determined by inspection, and used the material as delivered ; 
and secondly, that no hoes were used, all the men using the 
shovel as described, and each shoveller as he turned over his 
shovelful made three or four cuts into the mass with his 
shovel in a nearly vertical position, the object being to ram 
the mortar between and over the broken stone, and also pre- 
vent the mass from being heaped up, which would cause the 
stone to roll down to the base of the mass, and leaving a sur- 
plus of mortar on top. This operation was continued until 
every stone was covered. Mixing by hand is rarely economi- 
cal or rapid enough where large quantities of concrete are to 
be made in a limited time. The method of mixing mortar, 
together with the ingredients and proportions of the same, 
whether mixed by hand or machinery, are elaborately explained 
in Gen. Gillmore's treatise, pages 192 to 206 inclusive, to 
which for valuable information the reader is referred. 

24. The consistency of the mortar — whether very soft, in a 
pasty condition, or almost dry — is not explained. This is an 
important consideration, and one upon which there is a wide 
difference of opinion. In the Appendix to Gen. Gillmore's 
treatise he speaks of the mortar as being " about the consistency 
of plasterer's mortar." In an extended experience the writer 
of this work has found this consistency to give the best results 
in many ways, can be more readily incorporated, as well as 
more uniformly mixed ; can be handled more readily ; can be 
compacted by ramming without producing a spongy, springy 
mass; takes its initial set more readily; and certainly for ordi- 
nary purposes is more satisfactory, than when the mortar is 
more liquid, as well as when it is too dry and stiff. In the Ap- 



12 A PRACTICAL TREATISE ON FOUNDATIONS. 

pendix Gen. Gillmore gives some valuable information on the 
cost, qualities, and proportions of ingredients of concrete on 
Staten Island, which is well worth studying, as well as methods 
of mixing mortar and concrete by hand and machinery. Only 
one or two tables of proportions will be given. 
" Concrete No. I : 

i bbl. German Portland cement, } 5.4 bbls. concrete 
5f " damp sand loosely measured, f mortar. 
6 " gravel and pebbles from sea-shore, \ 12 bbls.; 
9 " broken stone, > 26 per cent 

) of voids. 

Producing 50 feet of rammed concrete. This concrete is of 
first-rate quality, being compact, free from voids, and strong. 
It is richer in mortar than would be necessary for most pur- 
poses." Proportions 1 mortar to 2^ stone and gravel — evidently 
a large excess of mortar over quantity necessary to fill voids. 
In the writer's experience 2 barrels of sand to 1 barrel of 
cement for ordinary and 3 barrels of sand to 1 barrel of Port- 
land cement seem to be the rule for use in constructing foun- 
dations for bridges of great magnitude. For less important 
work from 4 to 5 of sand to one of cement. 
" Concrete No. 5 : 

1 bbl. Rosendale cement, \ 

3 " damp loose sand, > 3.27 bbls. concrete mortar. 

5 " broken stone, ) 

Will yield 21.75 cu. ft., rammed in position." This mortar 
possesses a crushing strength of 130 lbs. per square inch when 
two months old. " Another proportion given : 

4 barrows of mortar (8 cu. ft.) ; 

6 heaped-up barrows of broken stone (14 cu. ft.); 

6 heaped-up barrows of gravel (14 cu. ft.)." 

This would seem a good proportion of ingredients. No mention 
is made of the resulting quality of concrete. 

25. It will be observed from the proportions above given 



FO UN DA TIONS. 1 3 

that Government engineers seem to prefer an admixture of 
gravel with the broken stone, — presumably to save mortar. It 
is rarely the case that gravel and stone can be economically 
secured at the same time, and consequently as a rule only one 
of these elements can be used ; and when it can be done the 
chances are that one part of the concrete will be largely of 
stone and the other largely of gravel, as there is no known law 
by which gravel can be forced to place itself between the 
pieces of stone. Either alone makes good concrete, as doubt- 
less a mixture of the two will ; but many would prefer the an- 
gular and rough broken stone to round and smooth gravel,, 
provided the stone is as hard as granite or limestone, or some 
of the varieties of hard sandstone. Broken bricks and shells 
are often used in localities where neither stone nor gravel can 
be found ; gravel would evidently be preferable to brick or 
shells. The mortar takes hold of the broken stone, thereby 
tying and binding the whole mass together, which does not 
take place when gravel is used, as can easily be seen by break- 
ing a block thus made : the gravel pulls away from the matrix 
or mortar, leaving round, smooth holes. For most purposes 
concrete has only to bear a crushing strain, and is not sub- 
jected to a tensile strain unless a foundation is undermined, 
which ought not to occur often. 

26. The writer has used over 30,000 cu. yds. of concrete, 
supervising to a considerable extent the mixing, in all its de- 
tails, personally ; but owing to the circumstances under which 
he was placed, it was impossible to give that particular atten- 
tion to exact proportions as might conduce to the very best 
results, but certainly good enough for the purposes intended, 
as it has stood for years bearing enormously heavy steady 
loads, and the heaviest known rolling loads running at the 
highest speed : therefore he can say that he has fully complied 
with all the conditions of good work, strength, durability, 
safety, with the least cost and time ; and even permanency 
can safely be claimed. He will therefore give the benefit -of 
his experience on such bridges as the Ohio River bridge, the 
Susquehanna and Schuylkill River bridges on the B. & 0„ 



14 A PRACTICAL TREATISE ON FOUNDATIONS. 

R. R., and the Tombigbee River bridge in Alabama, each of 
which will present some difference. 

27. Taking them in order. We used concrete resting on 
indurated clay; there were four piers resting on the concrete. 
The mortar was 1 sand, 2 cement, composed of a fair average 
sand, clean and sharp ; the cement used was known as the 
Louisville cement. These were mixed by hand in propor- 
tions of 1 cement and 2 sand, water sufficient to form a paste 
of the consistency of plasterer's mortar ; the sand and cement 
were thoroughly mixed dry by turning over and over with 
shovels. This mixture was then formed into a circular dam, 
and a small quantity of water was poured inside ; a portion of 
the dry mixture was pulled by hoes towards the centre and 
thoroughly mixed with the water, care being taken not to let 
the water escape, as it would carry the cement off. If this 
mixture was too dry, more water was added and thoroughly 
mixed, and this process continued until the entire batch was 
of the proper consistency. The broken stone was a hard 
bluish-gray sandstone found near by, and small enough to pass 
through a ring 2 inches in diameter — as close as could be ex- 
pected. A thin layer of this stone was spread on a platform, 
upon this a layer of mortar, on top of which another layer of 
stone, and then another of mortar ; this was then turned over 
and over with shovels as previously described, until every 
stone was coated with mortar; and it presented a uniform ap- 
pearance of mortar and stone mixed. On this work the mix- 
ing was generally done in the foundation pit, and the concrete 
was then thrown with shovels into layers of about 10 to 12 
inches thick, and rammed in place. A pine plank, 3 inches 
thick by 12 inches broad, cut in the form of a rammer, seemed 
to serve the purpose better than a round heavier rammer, 
suggested by ramming clay puddle. The ramming was con- 
tinued until a thin skim of water appeared on the surface, 
then another layer of concrete was put on top of this. Under 
some of the piers clean river gravel was used instead of broken 
stone, mixed and compacted in place as above, with equally 
satisfactory results. The proportions were usually 1 barrow 



FO UN DA TIONS. I 5 

■of mortar to 2\ barrows of stone, varied somewhat as the size 
of the stone varied. With a little experience the proportions 
would be easily adjusted by the eye, the aim being to have all 
the interstices filled. The broken stone was moistened. We 
secured a reasonably uniform result. The quantity here was 
not very great — 649 cu. yds. 

28. At the Susquehanna and Schuylkill River bridges all 
the concrete in the cribs above the caisson roof was mixed by 
machinery. All that portion of the concrete in the working 
chamber of the caisson was mixed by hand, as above described, 
only small quantities being used at a time. The concrete for 
the crib was mixed as follows : A revolving drum with buckets, 
similar to those on an overshot water-wheel, proportioned so 
as to carry 2 or 3 of sand to 1 of cement, fed through two 
distinct hoppers, dropped, as it revolved, the sand and cement 
into a trough in which was placed a revolving worm-screw 
about 10 feet long ; the sand and cement were carried around 
and forward, thoroughly mixing them dry ; at a certain point, 
determined by experiment, water was admitted from a spigot ; 
experiment determined how much was necessary to be admit- 
ted. Water, sand, and cement were now turned over and car- 
ried forward ; everything was so adjusted that at the end of 
the trough a paste of the proper consistency was found (this 
apparatus was the invention of Charles Sooysmith, one of the 
contractors). At the end of the trough the mortar dropped 
into the concrete mixer, which can best be described as about 
two thirds of an iron cylindrical pug-mill, 6 or 8 feet long, 
gently sloping downwards from the end of the trough, the 
arms of the revolving shaft in the mixer being so set as to 
•cause the materials in the mixer to be revolved over and over 
and at the same time moved forward. The proper proportion 
of the broken stone to a barrel of cement having been collected 
near the upper end of the mixer, it was shovelled into the 
mixer as the mortar dropped in from the trough. Intelligent 
men soon learned to shovel at a uniform rate, and would com- 
monly throw in with reasonable approximation the proper 
proportion of stone to mortar delivered. The concrete by the 



1 6 A PRACTICAL TREATISE ON FOUNDATIONS. 

time it reached the lower end of the mixer was thoroughly 
mixed, and then dropped into wheelbarrows and carried to 
the place of deposit. There were defects in this method. Ab- 
solute uniformity was not obtained, but even then we had a 
remedy : if the concrete when it drooped into the barrows was 
too wet or too dry, or had a larger proportion of stone than the 
mortar could carry, or not thoroughly mixed, it was thrown 
away, and the proportions readjusted. Some waste resulted ; 
some little time was wasted. The proportions aimed to be 
used were as I of mortar to z\ of broken stone. The concrete 
for these structures was generally dropped from a greater or 
less height, as the timber work was always built well ahead of 
the concrete ; but nevertheless it was distributed in layers with 
the shovel, and rammed as before described. 

29. The stone at the Susquehanna was granite, at the 
Schuylkill limestone, broken in both cases by the Gates crusher. 
No attempt was made to screen the stone ; the impalpable dust 
to a large extent was blown away; but the stone as it came from 
the crusher was delivered at the caisson, and consisted of stones, 
say from 3 inches in diameter through all sizes down to the 
size of coarse sand : this was taken into consideration in pro- 
portioning the sand in the mortar. The broken stone was 
generally kept moist, always in hot weather. In the crib of one 
of the piers at the Schuylkill, as a matter of economy, the crib 
was filled with what may be called rubble-work, one-man stones 
being simply imbedded in mortar. Great care is necessary in 
this kind of work to secure a solid, compact structure, and 
there is danger of great waste of mortar ; but why it should not 
be as good as concrete in large masses is probably hard to 
explain, as to some extent it does look like folly to break stones 
up simply t© cement them together again : but good practice 
does seem to lean towards concrete. At both of these bridges 
large stones (one-man stone) were placed at intervals on the 
surface of a layer of concrete and then covered over with an- 
other layer, of which, however, the writer doubts the wisdom. 
It may do no harm, but surely it does no good : it would not 
lessen the cost or the time. All concrete or all rubble is best. 



FO UN DA TIONS. 1 7 

30. As to the Tombigbee River bridge, located in the almost 
limitless swamps of Alabama, there was nothing especially 
notable, except its inaccessibility, and the almost total absence 
of building material of any kind, except we may say good pine 
timber. It is true a limited amount of gravel could be found, 
but this mixed with sediment from the frequent overflows. 
Good sand could be found in places ; the gravel had to be 
washed. We were compelled therefore to use broken brick, 
which had to be brought from Mobile on barges a distance of 
over a hundred miles ; a small quantity of broken stone left 
there by incoming vessels, which had been used as ballast ; con- 
sequently oyster-shells brought, by schooners hundreds of miles 
distant, from oyster-banks had to be relied upon, and this had 
to be provided and delivered at high stages of the water. The 
mixing was by hand as previously described ; there was nothing 
new or novel, except materials used. These materials for con- 
crete are the last resort of engineers, and of the two broken 
brick is the best. But much can be done with good cement 
and clean sharp sand. 

31. The following general principles should be observed in 
making concrete : 

Use good cement and clean sharp sand for the mortar, in 
proportions, depending upon the quality of the cement, of 2 
to 4 of sand to 1 of cement ; sufficient water to produce a some- 
what soft and plastic paste. 

Use the hardest stone available, granite, limestone, hard 
varieties of sandstone, gravel, etc. This to be broken as nearly 
as practicable so as to pass through a ring of 2 inches in 
diameter. Moisten the stones certainly in hot weather. Use 
somewhat more mortar than is necessary to fill the voids, which 
will depend upon the size of the stone, whether broken by hand 
or machinery, also upon the material ; but in general from 
2 to 4 volumes of broken stone to I of mortar. Mix thoroughly 
the sand and cement, and mix thoroughly the mortar and 
stone. 

Deposit the concrete in layers of not over 12 inches in thick- 
ness, and ram until a thin skim of water appears on the surface. 



18 A PRACTICAL TREATISE ON FOUNDATIONS. 

Mortar scarcely moistened is recommended by some engi- 
neers as producing ultimately the best result. 

3l£. In a letter from Gen. T. L. Casey, U. S. Engineer, the 
proportions of cement, sand, pebbles, and broken stone for the 
concrete sub-foundation of the Washington Monument were 
given as follows : 

" i volume of cement, dry; 

" 2 volumes of sand, clean, sharp, and medium size; 

" 3 volumes of pebbles, clean, and varying in size from a 
buck-shot to pigeon's egg ; 

"4 volumes of broken stone, clean, and small enough to 
pass through a 2-inch ring. 

" A ' batch ' consisted of f barrel of cement, i^ barrels of 
sand, 2\ barrels of pebbles, 3 barrels of broken stone. In dry 
weather about 10 gallons of water was used to a batch, but in 
wet, soaking weather no water was added. The ingredients were 
mixed in a cubical box 4 ft. on each edge, rotating on a diag- 
onal axis passing through the box. The mixer was turned 
eight times for each batch. The concrete when emptied from 
the box was about as moist as moist brown sugar. Three of 
these batches made a cubic yard. It required i-J bbls. of 
cement per cubic yard of concrete. Cost per cubic yard con- 
crete, $6.56." 

This concrete was very dry. The writer tried these propor- 
tions at the Susquehanna, except the pebbles, but found the 
concrete too dry to handle in large quantities and rapidly in 
a satisfactory manner, failed in getting the stones uniformly 
distributed when rammed in place, and after waiting for sev- 
eral days after depositing the concrete in the crib, found that 
no change whatever had taken place ; the sand and cement 
were still dry and separate, no set whatever had taken place, 
and the condition of the mass was the same as if broken stone 
was simply mixed with so much sand. After this more water 
was used, which seemed to be very much more satisfactory, 
both as to setting and ease of handling and compacting into a 
homogeneous mass. 

32. The proportions of cement to sand, and the proportions 



FO UN DA TIONS, 1 9 

of mortar to broken stone or stone and gravel mixed, seem to 
vary in the practice of engineers between wide limits, and all 
apparently produce satisfactory results; economy doubtless in 
most cases being the most potent factor, but necessarily con- 
trolled by the size of the stone used and the manner of breaking 
it, whether the stone is screened or not, and the importance and 
magnitude of the structure. In the first caisson sunk at Havre 
de Grace the stone was screened, using only the stone of con- 
siderable size. According to records kept, we used 2283 barrels 
of cement and made 1979 cu. yds. of concrete : this includes the 
large one-man stone used, the whole estimated as concrete, or 
1 barrel of cement made only about 0.9 cu. yd. of concrete ; 
whereas the average of the other four caissons, the stone not 
being screened, the average yield per barrel of cement was 
1.1 5 cu. yds. concrete. The entire work consumed 14,288 
bbls. of cement, mainly Portland, and yielded 14,966 cu. yds. of 
concrete, or practically 1 bbl. of cement to 1 cu. yd. of con- 
crete. The unscreened stone resembles closely the mass of 
broken stone mixed with gravel, and requires proportionately 
less mortar. 

33. In handling large masses of concrete an absolute rule 
as to proportions would hardly lead to anything more than 
approximately uniform results, as the same crusher will vary 
materially in the size of the stone broken from day to day, but 
with the same stone broken under the. same general conditions 
the variation might not be material. A simple method of 
determining the volume of voids in a cubic yard, such as filling 
a box containing one cubic yard of the stone, after allowing 
the stone to be soaked with water, then pouring in water suffi- 
cient to fill the voids : this volume of water gives the volume 
of mortar required to fill the interstices between the stone, to 
which a liberal excess should be added, as it is better to have 
too much than too little mortar. In some cases mortar alone 
is used to fill a crib. This is expensive, and to save money, 
mortar is thrown down in layers, and while in this condition 
large stones are simply thrown down upon it at random and 
then another layer of mortar, and so on. This necessarily fails 



20 A PRACTICAL TREATISE ON FOUNDATIONS. 

to produce a homogeneous mass, and unless the stones are 
carefully placed they will rest on each other, forming open 
spaces. 

Article III. 

USE OF CONCRETE. 

34. THERE are such a great variety of purposes to which 
concrete can be applied, that the principal ones alone will be 
mentioned. It is used to a large extent and almost exclusively 
for those parts of the substructure under ground and under 
water, in masses varying from 2 feet to 40 feet and more in 
thickness. 

In a subsequent article the uses of concrete will be more 
fully illustrated. The ease with which it is applied, the ease 
with which it can be made to conform to the irregularities of 
the foundation-bed, filling in under and around the irregular- 
ities, thus avoiding unnecessary blasting, hammering, etc., 
furnishes the simplest and most satisfactory means of spread- 
ing the base of the foundation, so as to reduce the unit 
pressure on the foundation-bed, and furnishing a uniform 
surface upon which to build walls of houses, piers, abutments, 
and other structures ; also forming water-tight floors and walls 
for cellars, lining reservoirs, cisterns ; the entire walls of houses 
can be built of it, and even entire piers, or filling in piers faced 
with masonry, iron, or timber. In all' of these cases it is in gen- 
eral more economical than rubble and brickwork, and certainly 
far superior to brickwork under ground or under water. 
Under walls of houses it is commonly not used in layers 
of over 1 to 2 feet in thickness, mainly to secure a base 
wider than the body of the wall in order to distribute the 
pressure over a greater area. Mr. Rankine, in his Civil Engi- 
neering, states that the limit of this widening depends upon 
the depth of the concrete, viz. : Take a wall of a house 2 
feet broad at the base and 20 feet long, this would give 40 
square feet of bearing surface if built directly on the foun- 
dation-bed, but by putting 2 feet of concrete and then building 



USE OF CONCRETE. 21 

the wall you can extend this concrete 2 feet on each side of 
the wall, forming a base 6 feet broad and giving a bearing sur- 
face of 120 square feet; if 3 feet thick a bearing surface of 
160 sq. ft. ; and so on. Upon this bed of concrete good rubble- 
work is commonly built to or a little above the surface of the 
ground, mainly as a matter of economy. Limestone is excellent 
for this, and better than sandstone, although the latter can be 
and has been used, either of which is more economical than 
granite. The writer thinks it unadvisable to use either sand- 
stone or brick under the surface of the ground unless cement 
mortar is used ; in fact health, comfort, freedom from damp- 
ness, demand cement to be used below ground in all cases ; 
economy alone says lime. Is it not better to be sure of the best 
foundation and economize in some other part of the structure ? 
Damp houses, cracked walls, doors and windows out of plumb, 
attest the truth of the above ; and what is more, how many 
walls actually fall before completion of the structure and after- 
wards, costing a thousand times more than was necessary to 
have put the foundation in properly. Sometimes timber is 
laid on the foundation-bed in two layers crossing each other : 
this is only admissible when a permanently wet stratum is 
reached. 

35. Concrete is used in large quantities under all important 
structures, and especially under bridge piers, abutments, re- 
taining-walls, etc., in masses varying in depth from 2 to 40 
feet, particularly in very deep foundations, where the pneu- 
matic caisson is used. This will be particularly alluded to when 
we come to discuss the subject of Pneumatic Caissons. It is 
also used to make enormous blocks of stone where, exposed 
to the action of immense moving forces, such as is in exposed 
conditions on the sea-coast, in constructing breakwaters, it 
would be very difficult if not impossible to transport blocks of 
the size desired. The concrete can be manufactured at points 
convenient to the site. Structures alluded to in the last para- 
graph will be discussed more in detail in another article. 

36. On the foundation-bed when concrete is omitted, or on 
the surface of the concrete when used, what may be called the 



22 A PRACTICAL TREATISE ON FOUNDATIONS. 

lower part of the body of the structure is constructed. This 
may be of brick or rubble, and in very large and important 
structures may be of first-class masonry, hereafter to be de- 
scribed in more detail. Brick is sometimes used, and is com- 
menced with one or more footing-courses, that is, courses pro- 
jecting from a quarter to almost one half the length of a brick 
— from 2 to 4 inches. This is not necessary when the wall 
springs from rock or a bed of concrete, as no spread of base of 
wall is necessary in this case, but is generally done. Outside 
bricks for projecting courses should be all headers : this is 
always done when the walls spring from clay or sand ; then 
above the footing-courses the body of the wall is carried up 
with the prescribed thickness. 

37. When this part of the work is of rubble the same rule 
is followed, except that the rubble wall is carried up to the 
surface of the ground with a little greater breadth than the 
body of the wall alone, so as to leave a small offset. When 
this part of the wall is under very large and important struc- 
tures, such as bridge piers, and is made of first-class masonry, 
there are generally several footing-courses, forming a series 
of steps so arranged as to leave a small offset just under the 
surface of the ground or water, where the neat work com- 
mences. The different kinds of masonry will be fully de- 
scribed, the proper kinds of bond and material used, and all 
technical terms used will be explained in another article. 

38. The crushing strength of concrete has never been fully 
determined, and in fact but few experiments have been made. 
Theoretically it should continue to harden indefinitely, and all 
that could be done would be to subject cubes or blocks to 
compression (noting carefully the kind and the proportions of 
ingredients) after the lapse of a certain time, and after inter- 
vals. This would give us the strength at that age, and by com- 
parison the rate of increase of strength ; but enough is known 
to establish the fact that it will in general acquire in a short 
time the strength of ordinary sandstone. It is claimed by 
some authorities that the set or hardening is delayed by press- 
ure. For this reason it is often prescribed that each layer 



BUILDING STONES. 23 

shall be allowed to set before adding another or before com- 
mencing the masonry. This cannot be done in large struc- 
tures on account of the delay that would be caused. The 
small amount of weight added each day could not cause any 
trouble. 



Article IV. 

BUILDING STONES. 

39. THE most important properties of rock suitable for 
building purposes are the Structural and Chemical. In regard 
to their structural character, they are divided into the unstrati- 
fied and the stratified, or those which show no distinct layers 
or beds and those that do show such layers or beds more or 
less distinctly. These properties are of great importance, as con- 
cerns both the strength, durability, and economy of structures. 
The unstratified rocks are generally the hardest and the strong- 
est, and can be obtained in immensely large blocks, but at the 
same time are expensive to quarry and dress into proper 
shapes; they are compact, and have a low absorptive power; all 
of which renders them valuable for structures of great magni- 
tude. Of these the most common are granite and syenite. The 
stratified rocks vary much in strength, durability, and compact- 
ness, and are formed in distinct layers, varying from the lami- 
nated or slaty structure in thickness, to that of several feet. 
The best kinds are hard and strong and durable, easily quar- 
ried, easily cut into desired shapes, and are widely distributed 
over the country, and consequently are our most useful and 
common building stones, are used in piers, retaining-walls, and 
walls of houses. Being found in many colors and combinations 
of colors, they produce a fine architectural and ornamental 
effect ; of the most common and useful are marble, limestone, 
sandstone, and slate. Each of these kinds will be considered 
in some detail. 

40. As to the chemical composition of stones, they are 
divided into three classes, viz., silicious, calcareous, and argil- 



24 A PRACTICAL TREATISE ON FOUNDATIONS. 

laceous stones, as these several substances predominate. The 
principal silicious stones are granite, syenite, and sandstone; of 
the calcareous stones, marble and compact limestone ; of the 
argillaceous stones, clay slate. 

41. Granite is unstratified and silicious, and consists of 
quartz, feldspar, mica, and hornblende. Its valuable properties 
are greater the more quartz and hornblende it contains, and less 
in proportion to the feldspar and mica contained ; but owing 
to its great hardness it is seldom used, except for building 
lighthouses, breakwaters, and large public buildings. Owing 
to its great cost it is seldom used in bridge piers, unless abun- 
dant and near at hand. Granite chips badly when exposed .to 
heat. 

41 1. Sandstone is stratified and silicious, and is composed 
of grains of sand commonly cemented together with a com- 
pound of silica, alumina, and lime. The best qualities of sand- 
stone are those in which the amount of cement tying the 
material is small and composed mainly of silica, and the grains 
are well-defined and angular. Much cementing material, when 
composed largely of alumina or lime, indicates a weak sand- 
stone, and especially if the grains are rounded. It exists in 
various degrees of hardness, compactness, strength, and dura- 
bility; is found of almost all colors, and makes beautiful and 
ornamental fronts to houses ; and being widely distributed, it 
is rendered at once the most useful and convenient of building 
stones. Owing to its more or less distinct stratification, its 
porosity, and consequently high absorptive power, it should 
always be placed in structures on its natural bed, so its layers 
may be perpendicular to the direction of the pressure ; other- 
wise the action of frost will cause disintegration and scaling 
off, as well as affording less resistance to the pressure ; and if 
much lime is present it decays rapidly when exposed on the 
sea-coast or to sulphurous vapors. 

42. It is generally conceded that neither a physical exam- 
ination nor a chemical analysis, or even an actual specimen 
test for crushing strength of a fresh-quarried stone gives even 
an approximate idea of its suitability for building purposes ; 



BUILDING STONES. 2$ 

but these combined with some other conditions, such as its 
appearance on exposed faces of large masses, should in general 
furnish satisfactory indications of its general properties. An 
exposed face of a mass of sandstone which we have good rea- 
son to believe has been exposed for a very long time should 
present the following appearance : The exposed surface should 
present a hard, rather dark-colored skin, of about an inch or 
two thick; the interior surface a little softer, and generally of a 
lighter color : this indicates a stone that hardens on exposure. 
All angle lines, vertical or horizontal, should be sharp and well 
defined. A rough exterior surface, with cavities of greater or 
less size and depth, with rounded corners or angle lines, indi- 
cates a soft variety of stone, and one that wears and disin- 
tegrates on exposure. 

43. The writer examined the sandstones bordering the 
Ohio River for many miles east and west of Point Pleasant, 
W. Va., and also many miles up the Kanawha River, in order 
to select a quarry for stone to be used in a bridge at that 
place ; and in this limit, although finding many kinds different 
in their properties, and getting all information possible from 
residents, he concluded that it would not be safe to risk the use 
of them in the large and exposed piers, and it was determined 
to use the Hocking Valley sandstone from a quarry over one 
hundred miles distant by rail: this was apparently the softest 
variety examined, was of a dark-brown color, and spawls could 
be easily broken in the hand ; exposed surfaces in quarries, 
however, presented a good appearance. A block of sandstone 
could be worked when just from the quarry with an ordinary 
pick. Our decision, however, was based on the fact that we 
found dams, piers, walls of houses, built of this stone, some of 
which we were informed had been built forty or fifty years 
prior to this time, and still bore the tool-marks, and were now 
found to be very hard ; consequently we used this stone to a 
very large extent. 

44. We subsequently found a quarry a few miles up the 
Kanawha River. This stone presented a favorable appearance 
in the quarry, and numbers of bowlders, some very large, were 



26 A PRACTICAL TREATISE ON FOUNDATIONS. 

found on the hillside which seemed to be harder than the 
quarry stone, and showing no signs of disintegration ; conse- 
quently some of the piers were built of this stone. The bowlders 
when large enough were freely used ; the color of this stone 
was something like rich cream. Another stone found near this 
quarry, on the other side of the river, of rather a bluish color, 
was extremely hard in the quarry, had a high compression 
strength when freshly quarried, but in parts of some structures 
built of this stone there were plain indications of scaling and 
disintegration : this was used to a very limited extent, and 
mainly for backing stone and in concrete. These facts are 
mentioned to show how uncertain appearances are, as well as 
the actual specimen test for crushing strength, unless the stone 
has been quarried for some time. It is always desirable, if 
possible, to know that a stone has stood the test of time in 
actual structures ; but often we have to do the best we can, 
guided by such tests and indications as above referred to. 

45. Sandstone may be then divided into two classes : those 
which, though soft at first, harden on exposure ; and those 
which disintegrate and decay on exposure, though they may 
be hard at first. The first alone should be used for building 
purposes. Sandstone stands exposure to fire better than 
granite. 

46. The writer collected a number of samples from the 
different quarries examined, and from each two or more speci- 
mens were carefully dressed into exact cubes 2 inches on edge 
each way, and subjected them to crushing, using smoothly 
dressed white-pine cushions cut of exact size of the cube ; these 
cushions, about one eighth to one quarter of an inch thick, were 
placed on top and bottom of cube to be tested. All the sam- 
ples tested by him were strong enough to bear any reasonable 
pressure, varying from 3000 to 5000 lbs. per square inch, and 
in general even the softer specimens of sandstone will stand 
the pressure ; but decay is the great danger to be avoided. 

47. Limestones, stratified and calcareous. Marble is gen- 
erally considered as a pure carbonate of lime, and is strong 
and durable and at the same time easily cut and dressed ; and 



BUILDING STONES. 2f 

from its variety of color in the same stone, as well as the 
variety of solid colors in which it is found, together with the 
high polish it will take, it is largely used for ornamental pur- 
poses, and also in many large public buildings as well as in 
private houses, but owing to its great cost it is not used in 
ordinary structures, and in addition it is not so widely dis- 
tributed ; yet marble quarries are claimed to exist in almost 
every State of the Union. Many limestones are susceptible of 
a high polish, and present a very beautiful surface, and are 
called marble for this reason. 

48. Compact limestone is what might be called an impure 
limestone, containing greater or less proportions of silica, 
alumina, and iron, or these combined ; and the qualities of the 
stone for building purposes depend more or less upon the 
amount of these foreign ingredients. But, generally speaking, 
any compact, hard, and fine-grained limestone is one of the 
most useful and common building materials. A loose, porous, 
limestone should not be used; however, some of the soft varie- 
ties are found to harden on exposure. These stones are often 
difficult to quarry and dress, and often cannot be obtained in 
anything like regular shapes, and are therefore useless for any- 
thing but rubble work. Other varieties occur in well-defined 
layers of thicknesses from 1 inch to 2 feet, are easily quarried,, 
require but little dressing, and are both economical and dura- 
ble ; should always be laid on their natural beds, and no excuse 
can exist for not doing so (in sandstones it is difficult to deter- 
mine in some varieties which is the natural bed). Its absorp- 
tive power is small, and therefore it is not liable to disintegrate 
by action of frost. It will not stand exposure to high tempera- 
ture, and is rapidly disintegrated in case of fires in cities. The 
p.ure varieties of limestone, when properly burned, yield the 
ordinary quicklime, and those which contain certain deter- 
mined proportions of silica and alumina yield hydraulic limes. 
Limestones effervesce with acids — a distinguishing charac- 
teristic. 

49. Argillaceous Stones. The only variety of these stones- 
of any value to the engineer is what is known as slate. Its. 



28 A PRACTICAL TREATISE ON FOUNDATIONS. 

principal use is for roofing houses. This is a stratified stone, and 
when it can be split into very thin layers it has what is said to 
be a laminated structure. It is found of several colors, but the 
darker colors in general indicate great strength and durability. 
It is almost impervious to water. 

50. A table of the resistance to crushing of these several 
kinds of stone has already been given. The absorptive power 
of these stones can be arranged according to a descending 
scale as follows : Sandstone, compact limestone, marble, and 
granite, — the two last practically absorbing no water at all. 
The absorptive power can be easily determined by weighing a 
specimen dry, and then, after being immersed in water for a 
reasonable time, the increase of weight will determine the 
amount of water absorbed. After removing from the water, 
the surface water adhering should be allowed to drip off. As 
to resistance to heat, the order may be taken as follows : Sand- 
stone, granite, limestone, the last being entirely decomposed 
under the influence of intense heat. 



Article V. 

QUARRYING AND STONE-CUTTING. 

51. It has been formerly stated that it is the duty of engi- 
neers to design and build structures suitable to the purpose in 
view, and it is easily in the recollection of the present genera- 
tion when the engineer, so called, was expected to know how 
to do almost everything in the way of utilizing and controlling 
the forces and materials of nature, in promoting the comfort, 
happiness, and prosperity of mankind ; and as at the period 
referred to but little was known, it was possible for one man to 
know and to put into practice what was known, — mainly by a 
sort of rule-of-thumb method. This perhaps may have originated 
the prefix Civil to the general term engineer. But in the past 
few years such development and progress has been made in 
the sciences and arts, that it has become necessary to divide 
the subject into almost numberless branches, all more or less 



QUARRYING AND STONE-CUTTING. 29 

allied and interlinked, but each so broad and deep that he is 
fortunate who has the time to master any one of its subdivi- 
sions ; and here we have the civil, the mechanical, the hydraulic, 
the city, and now the electrical engineer, to say nothing of the 
architect and the bridge engineer. Bridge construction has now 
become an almost exclusive science. Consequently it is difficult 
to know how much of each of these any one should know, in 
order to claim or deserve either of the above titles, and equally 
difficult to determine the border-line between any two of them. 

52. These considerations must be the writer's excuse for 
introducing several subjects that would seem to have not the 
least connection with what he shall give as a title to this vol- 
ume, namely, a Treatise on Foundations, and must at the same 
time explain the omission of many things that should be in- 
cluded. 

QUARRYING. 

53. Quarrying is purely an art, and little can be learned of 
it except by experience. The illiterate quarryman will take 
out more stone, and in better shape, in twenty-four hours, than 
the ordinary engineer will do in a month ; but still it seems 
that he should at least have the benefit of the few general 
principles that are known. All stones, even the granite, have, 
to the expert, well-marked division lines ; limestone and 
sandstone have them generally well defined, and the first prin- 
ciple in quarrying should be to detect these division lines, not 
only as a matter of economy, but also to obtain the blocks of 
the proper size and shape. Another principle is either to use 
no powder or very little explosive material, except in case of 
the very hardest kind of rocks, such as granite, and then with 
great care and judgment, as it is hard to determine the effect 
of an explosion upon the portions of the mass loosened, it 
may produce injurious effects, which may remain unseen and 
seriously impair the ultimate strength and durability of the 
material. However, blasting with powder or dynamite is usually 
resorted to, the large volumes loosened and time saved com- 
pensating for the waste caused by the explosion, and in addition. 



30 A PRACTICAL TREATISE ON FOUNDATIONS. 

a judicious use of small charges seem to produce better results 
than larger charges. Limestone in layers can generally be 
quarried by the use of picks, crowbars, hammers, and wedges. 
Sandstone can often be readily quarried by the same tools, 
aided by the use of the plug and feathers, which consist of a 
small steel wedge and two iron semi-cylindrical pieces ; but un- 
less the stratification is well denned, blasting is resorted to ; 
and often it is found advantageous to throw down very large 
blocks of the material, and subsequently subdivide these, 
either by small blasts, or by the use of the above tools. The 
plugs and feathers are used by first drilling a series of small 
holes a few inches deep in a line, then placing two feathers in 
each hole and driving the plugs between them. No attempt is 
made to drive each plug or wedge any great depth at any one 
time, but a blow of a hammer is given in succession on each 
plug in the line, and the stone will soon split entirely through 
the block along the line of the holes. 

54. When blasting is necessary, holes have to be drilled of 
greater or less depth, and varying in diameter from if to 2\ 
inches. These holes are then partly filled with a large- 
grained powder or dynamite, and exploded either by ordi- 
nary fuse or electricity; several, at distances apart depending 
upon circumstances, are fired simultaneously, and at definite 
times, such as at noon and at the end of the day, when 
the men can be away at meals, in order to have plenty of 
work ready when they return. There seems to be no fixed 
rule as to amount of explosive material used, as conditions 
vary greatly, even in the same quarry, and nothing but 
experience and good judgment can be depended upon ; an 
ordinary rule is to fill the hole about one-third full of powder. 
The hole should then be filled by first placing a few inches of 
dry clay on top of the powder. This clay should be free from 
sand or grit, and should be gently tamped or compacted with 
a wooden rammer, to avoid premature explosion. The hole 
can then be filled with sand or other rubbish. Results seem 
to show that from \ to 2\ pounds of powder are required 
to loosen thoroughly a cubic yard of rock in place. As 



QUARRYING AND STONE-CUTTING. 31 

generally stated, the mass of rock loosened bears some propor- 
tion to the line of least resistance cubed, and estimated at 
about twice that result, it being understood that that line is 
the shortest distance to the exposed face of the rock from the 
charge ; but this is often far from the fact, as this least re- 
sistance depends upon the nature and character of the material, 
the position and direction of the hole and the manner of 
tamping or filling the hole. 

55. The holes can be drilled or bored by hand or machinery. 
There are three methods by hand. In the first, a long iron rod, 
with a steel chisel-shaped cutting edge, is lifted by one or two 
men to a certain height and then allowed to drop in the hole, 
giving a slight turn after each blow. In the second, an iron 
rod of varying lengths, according to the depth of the hole 
required, is held by one man, and two men strike on the top of 
the drill alternately, the man holding the drill turning it con- 
tinuously as the blows are struck. The first of these is consid- 
ered more efficient. In the third, known in practice as " ball 
drilling," one man has a long iron rod, with a specially made 
point, this rod he simply lifts and throws into the hole, as it 
were. The accuracy with which they handle the drill and the 
rapidity of the work are certainly astonishing, and perhaps the 
reason that it is so seldom resorted to is that it requires the 
skill of a drum major to keep the hole straight and hit in it 
every time. A day's work in drilling will vary from 5 to 15 
feet per man. 

56. Machine-drilling is on the same general principles, ex- 
cept the power is applied by steam. The drills are moved 
forward by blows or turning, or both, and of course on exten- 
sive works progress is more rapid and economical than by hand- 
drilling. The diamond drill is in very common use, is expensive 
in its first cost, and rarely used when limited quantities of ma- 
terial are to be quarried. The tube or drill in this case is a pipe 
or hollow tube, having a head at the bottom, in which is placed 
number of small black diamonds, projecting slightly from the 
surface. This is caused to revolve rapidly and cuts a cylindri- 
cal hole. The material, in the form of dust or small particles 



32 A PRACTICAL TREATISE ON FOUNDATIONS. 

of the stone, is brought to the surface by forcing water down 
the tube through holes in the head and returning through other 
channels on the outside of the drill. In hand-drilling the 
debris or dust is removed in a very crude way — by first remov- 
ing the drill from the hole and inserting a long branch of some 
kind of wood, split and broomed at the end, or by the use of 
small wooden or iron spoons, connected to the end of a pole. 
During the process of drilling, water has to be continually 
poured into the hole. It aids the drilling by softening to some 
extent the material, and keeps the end of the drill cool. 

57. Dynamite has many times the explosive power of pow- 
der, varying according to the percentage of nitro-glycerine it 
contains, and is generally used in place of powder when a vio- 
lent and sudden explosion is required, as blasting in railroad 
cuts or in removing large masses, regardless of the shape or 
size in which they are thrown down ; but in quarrying for 
dimension stone great care should be used to avoid too much 
shattering of the stone and breaking into small pieces. Dyna- 
mite generally is sold in candles, so called, of almost any 
diameter and length, and containing different quantities by 
weight, wrapped in brown paper, which makes them convenient 
to handle, and apparently no more dangerous than powder, as 
certainly the men handle it as carelessly as they do the ordi- 
nary blasting-powder. 

58. Quarries should always, when practicable, be opened on 
hillsides, so as to obtain a large vertical working face, and the 
top soil stripped off until a solid ledge is reached over a con- 
siderable area. This stripping is generally expensive in first 
cost. This stripping can be done economically and rapidly 
with a water jet where water in sufficient quantities is con- 
venient, but the necessary machinery is expensive. 

59. The most economical condition for quarrying is when 
all of the stone, both large and small, can be utilized, as otherwise 
the waste will be very great. All things considered, the cost 
of the construction will largely depend on this, as in order to get 
dimension or face stone for piers there will necessarily be a 
large quantity of large stone unfit for face stone, and at the 



QUARRYING AND STONE-CUTTING. 33 

same time a large quantity of small stone, such as one-man 
stone, and spawls suitable for breaking into stones for concrete. 
Consequently, if a series of bridge piers can be so planned as 
to combine in the same pier all of these sizes and shapes, the 
cost of construction would evidently be lessened. In many 
cases this can be done consistently with the recognized and 
good practice, the broken stone and one-man stone used 
under ground and under water, and the large, rough stone used 
for backing in the piers : or in some of the piers the backing 
could be large stone and in others concrete ; or even a combi- 
nation of these in the same pier, alternating the courses, one 
course backed with large stone and another backed with con-* 
crete, the latter producing seemingly a stronger pier than that 
built by either of the other methods. Absolute uniformity is 
the common practice, and dependent, as has been stated, prac- 
tically, on the whim of the chief engineer. Surely common- 
sense would justify the combination pier, with knowledge before 
us that either independently has been used repeatedly and with 
satisfactory results. (See Plate II, Figs. 1 and 2.) Some engi- 
neers will not allow the backing stone to be of a different kind 
from the face stone, when either are recognized as good enough 
for the entire structure. One reason assigned is that different 
kinds of stone have different degrees of expansion and con- 
traction under changes in temperature. Probably the greatest 
differences in hardness and strength exist in granite and sand- 
stone. According to Rankine, granite expands .0009 of its 
length in a change of temperature of 180 Fahr., and sand- 
stone varies in the same range from .0009 to .0012 of its length. 
Or take 90 as probably the greatest possible range of tempera- 
ture likely to occur, and we have for extreme differences 
.00045 an d .0006. But this range of temperature in a mass of 
masonry is improbable, and the fact is that the expansion is 
microscopic. 

60. Many engineers put upon themselves onerous and often 
useless, if not harmful, duties, such as specifying for each pier 
of a bridge the exact size of each stone in a pier and in each 
course. This necessarily leads to delay, confusion, and expense. 



34 A PRACTICAL TREATISE ON FOUNDATIONS. 

A good quarry foreman always makes a diagram of each course 
in a pier, and can easily select from the supply in the yard 
such stones as will fulfil the conditions of good masonry, which 
are marked and forwarded, together with the diagram, to the 
site of the work, and only occasionally requiring any cutting, 
except for a closure, unless in case of rejection of the stone 
when delivered. These lengths and sizes may vary slightly 
from any arrangement that would be made by the engineer, 
but in ordinary massive masonry would present as good an 
appearance and have equal bond. The proper rule is to fix 
definitely your limits upon the sizes, extent of bond, propor- 
tions of headers and stretchers, and allow reasonable variations 
between them. Harmony will prevail, good work be secured, 
and money be saved. Onerous requirements, especially when 
evidently useless, produce often the exactly opposite result. 

6l. Almost all large and important works are done by con- 
tract, for the obvious reason that, all things considered, it can 
be done more cheaply and more expeditiously in this way ; and 
although the writer has met with rascals in almost all depart- 
ments of the contracting business, he is glad to say that he is 
not one of those who think that all or even a large majority of 
them can be considered as belonging to that class. On the 
contrary, he believes that they are otherwise; and he would 
rather have a reliable contracting firm to do work without close 
inspection, if the firm has confidence in his justice and good 
judgment, with reasonable requirements, than to conduct the 
work in accordance with the most onerous requirements and 
most rigid and ruthless inspection without such confidence. 



Art. VI. 

STEREOTOMY. 

62. Stereotomy, as the art of stone-cutting is called, is an 
important and interesting subject, as well as a difficult one in 
practice ; but it rather belongs to the domain of the architect 
than that of the engineer, and except in the ornamental parts 



STEREOTOMY. 35 

of structures, the forms used are simple and we may say, few 
in number. In ordinary and massive structures the surfaces 
are plane or cylindrical, circular or elliptic, and all the stones 
in the same structure are generally of the same shape where 
plane surfaces are departed from. The true " skew arch " 
is an exception, every stone having a different shape and 
size, and of several kinds of curved surfaces ; but as com- 
monly built the surfaces are either plane or cylindrical. The 
more ornamental parts of a structure require a profound 
knowledge of forms and combinations of forms, geometrical 
shapes and lines and the manner of constructing them on 
paper, templets and models; the skilled stone-cutter does 
the balance, and for the simple forms the more intelligent of 
these can do it all with a little aid in calculating the radii 
necessary. In ordinary structures all the stones have plane 
surfaces and the angles are right angles. In piers in rivers 
the ends are sometimes cylindrical, circular, or elliptical or 
wedge-shaped, and always when exposed to heavy flows of drift 
or ice. In arches the sides are plain. The bottom is a part of 
the surface of a cylinder; the top is generally left rough. 
The whole stone is the frustum of a wedge, the sides being 
slightly inclined, so as to conform to the direction of the radii 
of the arch. Ordinary templets or models used in cutting the 
surfaces of the stone are made of wood. 

63. The tools used by the stone-cutter are hammers of 
various sizes and weights — both ends blunt, or one end chisel- 
shaped or pointed, or both ends chisel-shaped or pointed, 
and some patent hammers, and in addition tools called the 
point and chisel. Stone-cutters generally provide their own 
tools. 

64. The work in general is performed by first cutting chisel- 
drafts around the edges of the stone about 1$ inches wide — 
these all in the same plane ; and by the aid of a straight-edge, 
a piece of timber about 6 feet long, 3 inches wide, and 1 
inch thick, the enclosed rough stone is dressed down to the 
same plane. For a curved surface two chisel-drafts are cut, 
one at each end of the stone, to conform to the templet, and 



36 A PRACTICAL TREATISE ON FOUNDATIONS. 

the intermediate rough stone cut out in the same manner* 
Intermediate chisel-drafts are cut if the stones are very large. 
Stone-cutters are generally charged with the loss, if by careless- 
ness they ruin stone in cutting. 

65. It is generally prescribed that the beds and joints shall 
be plane surfaces at right angles with each other. This is. 
seldom fully realized in practice, and a very slight concavity is. 
in some respects favorable. The straight-edge should be 
applied longitudinally, transversely, and diagonally to see that 
the stone is out of wind or not warped, and the surface of 
the stone should closely conform to the straight-edge. It is 
also advisable to dress the side joints a little slack ; that is, if 
stones 2 feet broad on bed are placed touching on the face, 
they should be open from \ to \ inch at the back : this favors, 
filling the joints easily. Stones are not required to be abso- 
lutely of the same width from face to back, and for the entire 
depth of the stone; this would be called close dimension 
stone, but it is generally specified that they shall be of the 
same width for 1 ft. to i| ft. from the face. The bottom bed 
of a stone should be cut strictly to the same plane over its- 
entire surface ; the top bed may have slight inequalities on its 
surface, as they will be necessarily filled with mortar, and 
it is generally allowed that the large backing stones may 
have from \ to 1 inch less thickness than the face stones, but 
should in general have almost as good beds. 

66. Sometimes a chisel-draft is required to be cut around 
the edges of the stones, to enable the mason to set the stones 
exactly over each other. A good clean-cut, straight pitch-line 
will answer fully for this purpose and cost less, but it is advis- 
able generally to cut this draft at the angles or corners of piers ; 
but this is not always done. The writer always determined 
the exact centre and laid off the masonry to calculated dimen- 
sions every fourth or fifth course, so as to avoid any possibility 
of the pier getting out of plumb. 

67. Stone-cutters are very apt to cut the stone so that it 
will not be as thick on the back as it is on the face. This 
should not be allowed, as it makes the mortar joint too thick 



MASONRY. 37 

under the stone. This should be carefully measured with a 
rule, or better with an instrument made as follows (Fig. 3) : A 
batten 3 or 4 feet long with a projecting piece at the bottom, 
and a sliding piece attached ; the projecting piece is placed 
under and against the stone; the sliding piece is then lowered 
to touch the stone on top and fastened ; this scale is then 
applied to several points front and back, which will readily 
show any variation in the thickness. The face stones in each 
course should have absolutely the same thickness or rise of the 
course. In most massive structures the face of the stone is 
generally left rough or rock face, and generally the extent of 
the projections is immaterial, but it is usual to limit it to 4 



A 



Fig. 3. — Gauge for Sizing Stone. 

or 5 inches ; but the ends of piers below high-water and for 
some distance above, where there is much drift or ice, should 
be dressed to a reasonably smooth surface, or even bush- 
hammered, — that is, dressed as smooth as possible, — and this 
should extend below the water. The stones are all cut to the 
proper batter in the yards, except for the stones of the foot- 
ing-courses. The stones for each pier are generally cut in 
advance of the building, and piled up at some convenient place, 
arranged according to courses as far as practicable, increasing 
in thickness of courses from the bottom to the top, — the inverse 
order from that in which they are to be used in the structure, 
— in order to avoid too much labor in handling. 

Article VII. 

MASONRY. 

68. It will be best to adhere strictly to the common classifica- 
tions, as generally understood in this and other countries. We 
shall, however, reverse the general order and commence with 
the inferior kind, as follows : Dry stone walls, ordinary rough 



38 A PRACTICAL TREATISE ON FOUNDATIONS. 

rubble walls, rubble walls in course, block-in-course masonry, 
ashlar masonry. There are also some combinations of these, as 
walls made with ashlar or block-in-course or brick, and backed 
up with rubble. The most usual and widely distributed stones 
for building purposes are granite, marble, limestone, sand- 
stone, and brick. 

69. Granite, owing to its extreme hardness, is seldom used 
except in the most important structures, such as lighthouses, 
large piers, and public buildings, when cost of construction is 
not considered. Marble, though not so hard, and can easily 
be worked into ornamental shapes, is likewise only used in 
buildings where the cost is ignored. Therefore for ordinary 
purposes we are compelled to rely upon the following stones. 

70. Limestone is one of the most useful, most generally 
used and widely distributed of the building materials, 
and can generally be relied upon. It is found in various 
conditions of stratification, from the gnarled and twisted to 
that of the most perfect layers, in various thicknesses from a 
few inches to two or more feet. In this condition it is easily 
quarried, comes out with good beds, requiring little or no 
labor in dressing and cutting, and can be gotten of almost any 
length and breadth. Its strength and durability depends upon 
its compactness. It will not stand a high heat, under which 
it disintegrates, and also when exposed to an acid atmosphere. 

71. Sandstone is also widely distributed, strong and durable, 
and can easily be cut, sawed, and dressed ; occurs in thick strata, 
and can easily be quarried in blocks of almost any dimensions, 
all of which conditions render it a useful and valuable build- 
ing material for almost any kind of structures, but withal one 
of the most uncertain and treacherous of stones, as it exists in 
all conditions of compactness and hardness ; but unfortunately 
the hardest varieties when first quarried may be the least 
durable, and some of the softest varieties, which can be dressed 
with a pick when first quarried, prove ultimately the most dura- 
ble. Those varieties which present sharp grains with a small 
amount of cementing material are generally the best. The 
safest plan, however, is to examine structures, chimneys, steps,, 



MASONRY. 39 

etc., built of this material and known to have stood for a long 
period of time. These can generally be found, but in the ab- 
sence of this guide we have to do the best we can. Sandstone 
is porous, and special care should be taken to build it on its 
natural bed, but in many varieties of sandstone it is hard to 
determine the direction of the stratification. Mineralogy will 
give the color, general appearance, and locality where found, 
and other general properties. Chemistry will enable the 
reader to determine the exact composition, and engineers 
should be reasonably familiar with these subjects. 

72. Dry stone walls, although not capable of bearing any 
great weight, unless constructed of regular-shaped stone, with 
good beds, are useful for retaining-walls of small height, and 
can be built of almost any shape and size of stone, and even 
of round river jacks or bowlders, and answer well in those cases 
where no danger or risk could occur if they did fall down, and 
where great economy is desired. 

73. Rough rubble masonry is built of any shaped stones, just 
as they may come from the quarry, without hammering or any 
kind of dressing ; but generally one or two man stones down 
to the smaller spawls are laid without regard to continuous 
horizontal joints or beds, but with special care to breaking 
joints vertically, by overlapping the stones, producing what is 
called " bond," and well bedded in mortar, generally of common 
lime and sand ; vertical joints are also filled with mortar, and 
any openings between the larger stones on the beds or joints 
should be filled with smaller stones bedded in mortar. Thus 
built, it will make a wall of considerable strength, especially if 
built with cement mortar, and in the latter case will make a 
good arch ring for small arches, its strength somewhat exceeding 
the strength of the mortar used when hardened ; and when 
faced with a good coating of stucco or cement mortar, can be 
made to present a neat face. This kind of work is used in the 
lower part of foundations to carry even very heavy loads, and 
is suitable for ordinary retaining-walls, and for many purposes 
where economy is a matter of importance. 

74. Rubble walls in courses. In this class of work there 



40 A PRACTICAL TREATISE ON FOUNDATIONS. 

are no regular courses of uniform thickness, the joints between 
the stones, both in vertical and horizontal planes, being broken. 
The side joints need not be vertical, and the stones may be 
only hammer-dressed on joints and bed ; but with good mortar 
and reasonable care in building so as to have a good bond, this 
class of work can be made strong and durable, and, where 
looks are not considered, would answer almost any ordinary 
requirement, and may be made to harmonize pleasantly with 
rustic surroundings, and possesses one important element — 
economy. To a large extent the sizes o'f the stones used are 
unimportant, from very large to very small. It is the kind of 
masonry almost exclusively used for backing retaining-walls. 

75. A better class of this kind of work, in which the beds 
and joints are dressed, makes a strong and durable structure. 
The irregularity in the size and shape of the stones, provided 
the joints between the stones are broken horizontally and 
vertically, the rough undressed face of the stone, all com- 
bine to produce a fine architectural effect ; some of the 
handsomest churches and other structures are built of this 
class of masonry, though hardly to be recommended for heavy 
structures or structures subjected to forces tending to drag or 
knock the smaller stones out of place, such as bridge piers, 
which have to stand blows and shocks from driftwood, ice, etc., 
will form nevertheless a substantial and economical structure 
for ordinary purposes. 

76. To build this class of work great care must be taken to 
secure good bond, both longitudinally and transversely, and 
due care should be given to proper adjustment and distribu- 
tion, over the entire surface, of the larger and smaller stones. 

77. Block-in-course work. This class of work varies from 
the above in having regular courses of uniform thickness, 
varying from six to ten inches. The stones are cut into regular 
blocks of prescribed length and breadth, the length about three 
times the thickness and the breadth from one to two times the 
thickness, beds and joints cut true and at right angles to each 
other. About one fourth of the faces should show headers, — that 
is, stones whose ends show on the face of the wall and extend 



MASONRY. .41 

at least three times the depth of the course into the wall, the 
breadth of the headers being at least equal to the thickness of 
the course, — and they should rest on the stretchers below as 
nearly over the centre as possible, so as to allow for overlap or 
bond of at least one third of the length of the stretcher, the 
stretcher being a stone the length of which is shown on the face 
of the wall. Sometimes stones are found in strata of the thick- 
ness requisite for this kind of work, are easily quarried, do not 
require an excessive amount of cutting and dressing, and con- 
sequently are well adapted to the purpose. Sandstone and 
granite are generally quarried in much thicker blocks, and are 
therefore better suited to structures requiring thick courses, 
and can be more economically used in the larger blocks. 
This class of work is suitable for almost any structure, unless 
exposed to some kind of shock, as in case of lighthouses and 
bridge piers, and presents a neat appearance, but is not econom- 
ical unless the stone comes in the quarry in small blocks and 
with good natural beds. 

78. Ashlar Masonry. This class of masonry stands at the 
head of the list, and is used in all important structures, such as 
large piers for bridges, lighthouses, breakwaters, and large pub- 
lic and even private buildings. Granite is used for the most 
important structures regardless of cost, but limestone or sand- 
stone are used when cost enters as an important factor. The 
strength of this class of masonry arises from the large size of 
the blocks used, the care taken in cutting and dressing the 
stone, the care taken in building the structure, and the extent 
of the bond obtainable, both longitudinally and transversely. 
It is laid in regular courses, of thicknesses varying from 1 to 3 
feet. The length of stones from 1 to 4 times the thickness and 
breadth from I to 2 times the thickness, and with a bond 
from 1 to \\ times the thickness. The side and bed joints are 
dressed to plane surfaces and at right angles to each other ; it 
is not desirable that these should be perfectly smooth surfaces, 
but should present a series of shallow ridges and hollows, 
such as would naturally result from finishing with a pointing 
tool. They should be nearly true throughout the surface to 



42« A PRACTICAL TREATISE ON FOUNDATIONS. 

a straight-edge, rather concave than convex towards the centre 
of the surface. There is little danger of stone-cutters leaving 
the stone convex on the surface, as it is difficult to set such a 
stone, and tends to leave large open joints on the face. The 
danger, however, is of cutting the face concave, thereby insuring 
a thin and neat joint on the face. The danger here is of throw- 
ing the pressure on the edges of the stone, causing the edges 
to chip and spawl off, thereby defacing the face of the work. 
If resulting in no other harm, this effect can be seen on the 
face of many structures. 

79. Ashlar masonry, however, in large piers is only used 
on the two faces and two ends, leaving a hollow centre space ; 
this must be filled up with something. This filling, whatever it 
is, is called " backing," and depends to a large extent on the 
whim of the chief engineer. Some engineers say ordinary rubble 
is good enough, some say concrete ; some say large stones of 
the same thickness as the face stone, only leaving small space 
of from 6 to 12 inches to be filled with rubble or spawls. Few 
however, require the backing stones to be dressed as closely as 
the face stones, but they should be brought to a good average 
even surface on the beds, though some require the backing 
stones to be dressed as true as the face stones. This latter 
may be best, but if the other is good enough, why go to the 
greatly increased cost. The only reason that we can build 
ashlar masonry at the prices now existing is based upon the 
rough backing being used, as the profits are drawn almost 
entirely from this source. (See Plate II, Figs. 1 and 2.) 

80. The joints in ashlar masonry to be filled with mortar 
vary from ■§■ to -§ inch in thickness on the face. In actual 
practice, except in some special cases, the larger limit is prob- 
ably reached in most cases ; there is no need of exceeding 
this limit. 

81. Assuming that the face stones have been laid with the 
proper proportions of headers and stretchers, how shall the 
enclosed space be filled ? The writer would fill with large 
backing stones of the same thickness as the face stones, filling 
the small vacant spaces with spawls. A bad habit of masons in 



MASONRY. 43 

this filling is to put down a pile of small stones, then smear a 
little mortar over the top. This should not be allowed. A thick 
bed of mortar should first be thrown in, and the small stones 
pressed and rammed into the mortar, then another layer of 
mortar and stones pressed in, and so on. This insures solid work, 
and is as easily done, if not more so than the other. The spaces 
need not exceed 6 inches on an average. The backing stone 
should be laid so as to break joints both longitudinally and 
transversely. (See plan of pier, Plate II, Fig. i.) 

82. The practice with some engineers, after laying the 
large backing stone in place, taking care in all cases to break 
the joints in both directions, so as to bond the entire wall both 
longitudinally and transversely, is to fill the vacant space with 
broken stone of varying sizes, and then " grout " the work, 
that is, pour liquid mortar into these places until they are 
filled, first pouring in a liberal quantity of water; when filled 
with mortar the water will rise to the surface. The trouble is 
that under these conditions the cement and sand will to a large 
extent separate, the cement rising to the top, thus forming a 
series of layers of sand with little cement and of cement with 
little sand, as the sand will invariably sink to the bottom. This 
at least is the writer's experience. Others claim that it is best 
and insures a solid wall. It is largely practiced. 

83. The second-best method is to fill the entire space 
between the face stones with good concrete, with headers 
reaching well back into the wall and some backing stone over- 
lapping the tails of the headers from opposite faces. It has 
always been a puzzle to the writer why this plan is not more 
generally followed : it would certainly insure a solid strong wall, 
is more rapidly put in and probably more economical than the 
first plan, but some prejudice exists against it. (See left half 
of plan, Fig. 2, Plate II.) 

84. Lastly, to fill the vacant space between the face stones 
with rubble. This can be done either by carefully bedding 
the larger stones in mortar, and filling in between these with 
smaller stones and spawls well pressed in the mortar, or by 
simply throwing large and small stones in the vacant space 



44 A PRACTICAL TREATISE ON FOUNDATIONS. 

until filled, then pouring grout over the entire space until 
all interstices are filled with mortar, as above directed. This 
method is doubtless less costly than either of the other two. It 
may be good enough, but for some, no doubt good, reasons is 
rarely adopted for important works. (See right-hand half of 
Fig. 2, Plate II). 

85. In whatever manner the backing is constructed, the wall 
of the pier is carried up from course to course, each course 
being entirely completed before beginning another course, as 
it is a bad plan to build a part of several courses and leave a 
series of steps, and then build up the rest of the pier bonding 
•on the older work, which can rarely be done as well as in com- 
pleting entirely each course. 

86. The neat work commences at or a little below the sur- 
face of the ground or water, on top of the footing-courses 
which was called the foundation, and generally diminishes in 
size gradually to the top of the wall. This gradual decrease in 
length and thickness is called the batter, and is generally at 
the rate of \ inch to the foot all round, or in other words 
diminishes in length and breadth 1 inch for each vertical 
foot from bottom to top. The bottom dimensions are deter- 
mined from the top dimensions, which are fixed according to 
the purpose for which the structure is intended. In case 
of piers this is fixed by the bridge companies who build the 
iron work or superstructure, and adding 1 inch for each ver- 
tical foot of height gives the dimensions for the neat work at 
the bottom. The spread of the footing-courses is determined 
arbitrarily, but generally arranged so as to give from 2 ft. to 
one half of the bottom width of the neat work on each side, 
the projection of each course generally being from 6 in. to 9 
in., or even 12 in. The footing-courses generally increase down- 
wards by offsets or steps. 

87. The appearance of the stone on the face of the work 
has nothing to do with the classification of the masonry, this 
depending entirely upon the size and shape and the manner 
of dressing the beds and the joints of the stones. As to the 
appearance on the face, whether dressed smooth, as in the 



MASONRY. 45, 

finest of masonry, such as large public buildings, lighthouses, 
etc., or with-chisel drafts from 1 to \\ inches cut all round 
the edges of the stone, the remaining portion being left with 
quarry or rock faces, or whether a simple pitch-line is cut 
around the edges of the stones, that is, simply cut to a sharp,, 
straight, well-defined line, and the entire face left rough, except 
that projections over 4 or 5 inches are knocked off, — none of 
these conditions affect the strength or durability of the struc- 
ture." The chisel-draft aids in setting the stones true, the one 
above the other, so as to avoid slight projections, and enables. 
the mason to keep a regular and uniform batter. 

88. A good pitch-line fully meets these conditions. It is. 
considerably more economical, and in large masses of masonry 
permits a better and more appropriate appearance than the two 
first methods. For architectural effect, as well as to prevent a. 
continuous flow of rain-water down the face of the pier, at 
some suitable point a string-course is built in the wall; this, 
consists of broad stones well bonded into the wall and pro- 
jecting from 6 to 9 inches from it all around, with a wash 
cut on the projecting portion, that is, cut on a gentle slope 
downwards. At the top of the wall is placed a course of large 
stones projecting from 6 to 9 inches all round the wall ; a 
wash is also cut on the projecting portion : this is called the 
coping, the object of which is to give a neat finish to the top 
of the pier, to protect the smaller stones and rougher work 
below, and at the same time to distribute over a large surface 
the heavy concentrated weight above. These stones are 
dressed perfectly true and square on all sides, and laid with as 
close joints as practicable, these joints being entirely filled 
with a thin grout. The stones, owing to their exposed posi- 
tion, are generally fastened to each other by iron cramps, or 
fastened to the masonry below by long iron bolts, placed in 
holes drilled for the purpose and fastened in place by pouring 
. in the holes after the bolt is in place either melted sulphur, 
melted lead, or cement grout. On top of this coping another 
coping-course is sometimes laid, and then large thick stones of 
some hard material are placed (that is, in case of bridge piers) r , 



46 A PRACTICAL TREATISE ON FOUNDATIONS. 

from each of which springs an end post of the bridge with its 
pressure concentrated on this stone. This large stone is called 
the bridge seat or raising stone, and distributes the pressure 
over three or four coping-stones below, but otherwise is simply 
a matter of convenience, and is often entirely omitted. 

89. The appearance of a wall of masonry, on its face, does 
not necessarily determine the character of the masonry. It 
may look well, and seemingly in accordance with the specifica- 
tions ; the headers may only be blocks, or " bobtails," as they 
are called ; stretchers may have less breadth than thickness, 
and the interior bonds may be poor ; that this not only may be 
the case and often is, cannot be doubted or denied. The inte- 
rior condition is only fully known by the builder, the most rigid 
inspector cannot ordinarily prevent it, but mutual confidence 
and reasonableness between the two will largely do so. It is 
not unusual to specify that the headers and stretchers should 
not be less than 3 feet long, and likewise that they should not 
be more than 6 feet long. As to the length of the headers, it 
would seem better to proportion this to the thickness of the 
wall at that point. Walls are generally built in courses of 
varying thickness, and generally decreasing from bottom to 
top, the thicker courses being at the bottom, and the width of 
the piers varies from 15 feet to 20 feet at bottom to 6 feet to 
12 feet at top ; and with the limitation that a header should 
never be less than 3 feet long, the headers should generally 
vary, from 6 feet at bottom to 3 feet at top of the wall. A 
3-foot header in a course from 2 to 3 feet thick would practi- 
cally be of no use, but in a high pier it would be difficult to 
build it without securing a good bond throughout. 

Article VIII. 

ORNAMENTATION. 

90. Although ornamentation is of secondary consideration 
in large massive structures such as bridge piers, yet a good 
effect can be produced by a simple string or belt course at 
some suitable point in its height. This is, however, seldom 



ORN AMENTA TION. 47 

used with square ended piers, but with rounded or pointed ends 
it is usual. The curved or pointed end is generally built to a 
point a little above high-water, and the upper part is completed 
to the top of the pier with square ends, which is then finished 
off with a suitable coping. The string or projecting course is 
usually placed at the dividing line between the rounded and 
square end of the pier, and a low conical-shaped finish on top 
of the belt-course makes this passing from the one to the other 
pleasing to the eye. To make the templets, a platform of 
wood is made, a centre point fixed ; a round iron pin is then 
driven at that point, and a straight-edge laid flat, with a small 
hole near one end, can be made to revolve around this as a 
centre : another hole is bored at a distance from the first equal 
to one half the width of the pier at the bottom, and a spike or 
pencil fastened in this will describe a proper circumference on 
the platform, from which the templets can be cut. A pencil in 
other holes \, 1, or i|- inches from each other, according to the 
batter and the thickness of the course, will describe the proper 
circle for the different courses. (For circular ends see Plate II, 
Fig. 1.) 

91. For elliptical ends they may either be a part of one 
ellipse whose conjugate axis is the width of the pier, or some 
portion of the semi-ellipse, the double ordinate or base of 
which is the width of the pier, in which case the foci are 
marked on the board at a distance apart to be determined by 
the shape of the point and the length of the rounded end re- 
quired, which will be largely a matter of taste. At the foci 
drive spikes, and with a string equal in length to the trans- 
verse diameter of the ellipse, its ends fastened to the spikes, 
then with a spike or pencil, drawing the string tight and keeping 
it taut all the time, the pencil will describe the ellipse ; select- 
ing a point on the curve, whose double ordinate is equal to the 
width of the pier, this will be the base of the templet, which 
then must be cut to conform to the curve of the vertex of the 
ellipse. Sometimes the ends are formed by parts of two in- 
tersecting ellipses, which must be similarly constructed on the 
platform. The sizes of these, as said above, are mere matters 



48 A PRACTICAL TREATISE ON FOUNDATIONS. 

of taste : the length from the body of the pier to the point 
is generally about equal to the one-half width of the pier. For 
triangular ends, the sides are plane, the base is equal to the 
width of the pier, and the altitude equal to one half that width. 
(For elliptical and triangular ends see Fig. 2.) 

92. All of these ends, called starlings or cutwaters, are 
dressed on the exposed surfaces either smooth or approxi- 
mately so, and are generally carried up with the regular batter 
of \ inch to the vertical foot, and are placed generally at both 
ends of the pier for symmetry, but they are only necessary at 
the up-stream end. These portions of the pier are not consid- 
ered as bearing any part of the weight of the structure, but to 
split and turn aside drift and ice, or in some cases to prevent 
any scouring tendency by offering less resistance to the cur- 
rent. They should, however, be carefully bonded into the pier, 
and in some cases it is best to bolt them to each other. In 
some cases looks are thrown aside, and a well-defined cut- 
water is placed at the up-stream end of the pier, the lower 
being square. 

93. A strictly called cut-water is built on the up-stream end 
alone. This is used where the piers are very high and thick, 
and large masses of ice have to be dealt with. This is 
built from a little distance below low-water to a point a little 
above high-water — generally not over 12 or 20 feet. It 
may be described as an oblique pyramid projecting from the 
body of the pier, the up-stream edge sloping towards the 
pier at an angle of forty-five degrees. Near this edge the 
sides are dressed smooth, forming a sloping prism, whose 
base is a triangle, the base of which triangle is the width 
of the pier and the altitude one half to one time that width. 
The remaining portion of the cutwater is solid masonry, of the 
same width of the pier; the end stones should be thoroughly 
fastened to each other by iron bolts and cramps. This form 
of starling will split and break immense sheets of ice of great 
thickness. (See Plate XXII, Figs. 1, 2, and 3.) 



ICE AND WIND PRESSURE. 49 

Art. IX. 

ICE AND WIND PRESSURE. 

94. In piers of bridges, under normal conditions, the press- 
ures are vertical, and as the centre of pressure is in the centre 
of the figure of the base, the pressures are uniformly distrib- 
uted ; hence there is no danger of sliding, as the bed joints are 
horizontal or perpendicular to the pressure, and no danger of 
overturning, as the pressures are all vertical, and the piers only 
have to be strong enough to resist crushing. But under some 
circumstances they are subjected to unusual forces, such as high, 
winds, which not only act directly against the pier, but upon 
the superstructure and upon the train that may be passing 
over the bridge ; also from the current acting upon large fields 
of ice, which sometimes gorge or bank up to the depth of many 
feet; and when a solid mass bridging the river exists, each 
pier is supposed to carry a pressure due to a mass the depth 
of the ice by length of a half span on either side, and from 
the wind pressure that is exerted on the truss and train for 
the length of a half-span on either side. Both of these pres- 
sures are unknown, but by assuming values for these based 
upon such data as we have, the problem is a very simple 
one. Trautwine states that the pressure per square foot 
exerted by the wind upon a surface exposed at right angles to 
its direction is equal to the square of the velocity in miles per 
hour multiplied by the area of the surface and divided by 200, 
viz., F 2 A -f- 200 = pressure in pounds per square foot, at 40 
miles per hour, and A = 1 sq. ft., the pressure per square foot 
is equal to 8 lbs.; and for V — 100 miles per hour, the press- 
ure per square foot equal to 50 lbs., and so on. A velocity of 
100 miles per hour is a hurricane. The pressure from the field 
of ice or gorge is certainly unknown. The ice in the Susque- 
hanna River at Havre de Grace often freezes to the thickness 
of 2 feet. The writer has seen it from 15 to 20 inches thick in 
a solid sheet from shore to shore. It moves in this solid mass 6 



50 A PRACTICAL TREATISE ON FOUNDATIONS. 

or 10 feet at a time, and repeadedly, before it breaks up. The 
cutwaters on these piers would split it from 50 to IOO feet 
above the pier, the mass rising up over the cutwater; and 
while this was going on the broken ice from a distance 
above would be rising on top and sinking under this im- 
mense sheet of ice to unknown depths. These facts are 
mentioned to show the enormous and unknown pressure to 
which these piers are subjected nearly every winter. This 
probably represents as great a pressure from this source as 
is likely to occur anywhere, and as showing that piers as 
built from necessity are sufficiently large and heavy to resist 
all these outside forces. Some authorities give about double 
the pressure from the wind as above given, but by assuming 
50 lbs. per square foot of exposed surface it is doubtless on the 
safe side. 

95. As bridge trusses are open work, it is generally as- 
sumed that the exposed surface is double the area of one 
truss for an unloaded truss, and on a loaded structure 30 lbs. 
wind pressure per square foot of total truss surface, and in 
addition an equal amount per square foot of train surface, the 
latter treated as amoving load ; and as the good practice, though 
far from uniform, we may take truss and train as exposing 
together 20 square feet per foot of length, equivalent to 
600 lbs. pressure per foot of length, and for a pier carrying 
two 525-ft. spans, a total pressure of 315,000 lbs., equal to 
160 tons. Assuming that the pier splits the ice for a dis- 
tance of 50 feet above the pier, the ice being 2 feet thick, 
and assuming the resistance to be 10 tons per square foot, we 
would have 50 X 2 X 10 = 1000 tons. Moment of overturning 
due to wind pressure = 160 tons multiplied by lever arm 
(height of pier plus one half of truss, equal to loo plus 30 equal 
to 130 feet) = to 20,800 ft.-tons. The ice-pressure at the 
Susquehanna was doubtless the greatest at a rather low stage 
of water, but for safety we can assume the lever arm to be 20 
feet. We have IOOO X 20 equal to 20,000 ft.-tons ; but double 
this and make it 40,000 ft.-tons, there results then total over- 
turning moment equal to 60,800 ft.-tons. The weight of one 



ICE AND. WIND PRESSURE. 51 

of the piers would equal 4350 tons, and the weight of one half 
span on either side, or one entire span, say 700 tons, and weight 
of empty train and cars, 200 tons, or total 5250 tons, which 
multiplied by one half the length of pier, equal to 20 ft., then 
the moment of resistance to overturning, would be 105,000-ft.- 
tons, or a factor-of-safety of about if. These results are based 
upon the most unparalleled conditions, by increasing the ten- 
dency to overturn far beyond that which is likely to arise, as 
probably extreme pressures are assumed, and these supposed 
to act together, which would rarely occur, and the train is 
supposed empty in addition. The increased crushing pressure 
is not worth considering. The stability of pivot piers is cer- 
tainly equal to if not greater than that of the corresponding rest 
piers, and in addition they are protected from ice pressure by 
guard piers especially constructed and entirely separate from 
the pier itself, which serve also as rest and protection piers 
to the ends of the draw-span when open. These guard piers 
are built of masonry, iron, or timber. They are also required 
above and below both pivot and rest piers in some cases, and 
when built of timber or masonry faced with timber act as 
guiding dikes for the passage of vessels and steamboats ; 
when detached masonry guard piers are used, a floating crib or 
strong box is built between the guard piers and the pivot pier, 
which rises or falls with the water, being connected with the 
pier by properly arranged sliding surfaces. 

96. The top dimensions are fixed by the bridge companies 
so as to allow ample room for the superstructure, but in gen- 
eral for piers the dimensions vary according to the length of 
span, from 6 feet by 20 feet to 12 feet by 40 feet, and the 
bottom dimensions of the neat work are fixed generally by 
allowing one inch for each vertical foot, but sometimes by 
abrupt enlargements in addition. Pivot piers are generally 
round, and vary at top from 20 feet to 30 feet, so as to allow 
ample margin for the turntable arrangements. 



52 A PRACTICAL TREATISE ON FOUNDATIONS. 

Article X. 

RETAINING-WALLS. 

97. Ordinary earth will not stand for any length of time 
with a vertical face, but will generally assume a slope more or 
less steep, according to the nature of the material, the angle 
of this slope is determined by the adhesion between the par- 
ticles composing it and the friction between these particles or 
grains. The adhesion between the grains is destroyed by the 
disintegrating effects of air and moisture, therefore we may 
say that friction alone determines the angle of the slope. The 
angle which this slope finally assumes, measured from the hori- 
zon, is called the " angle of repose ;" the slope itself is called 
the " natural slope." When an earth embankment either 
reaches this slope from natural causes or is built with this 
slope, its stability is insured. The effects of running water, 
from rain or other causes, will wash it in ruts and gullies, but 
this can be provided against by sodding, paving, or good drain- 
age. 

98. It is often necessary, however, to maintain a vertical 
face, as behind abutments when the approaches of the bridge 
are built of earth, as well as in other similar cases. It 
then becomes necessary to build a wall of some kind, called a 
retaining-wall, or in case of supporting the pressure of water, a 
reservoir wall. The principles of stability of these walls are 
the same. 

99. The resulting force acting on a retaining-wall, or the 
abutment of arches, is always inclined to the vertical, more or 
less, depending upon the relative intensity of the weight of the 
wall acting vertically through the centre of gravity of its mass, 
and the intensity of the pressure of the earth on the wall, 
together with its direction. This obliquity of the resultant 
force causes two tendencies : the one is to cause the wall to 
slide upon the foundation-bed or upon some bed of the wall 
itself, the other is to overturn the wall bodily around some 



RE TA WING- WA LLS. 53 

axial line. The first tendency can easily be provided against 
by so arranging the foundation-bed, or some courses of the 
masonry, that their direction may be perpendicular to the 
direction of the force or pressure. A horizontal foundation- 
bed will generally give security against this tendency, unless 
the wall rests upon slippery and inclined layers of earth. 

100. The tendency to overturn can only be resisted by suffi- 
cient thickness and weight of wall to fulfil the two following 
conditions: 

ist. That the direction of the resultant pressure must not 
pierce the foundation-bed further from its geometrical centre 
than a certain limit, which may be taken at three eighths of 
the thickness. This point is called the " centre of pressure." 
This mode of stating the condition is a substitute for a factor- 
of-safety, as the actual point of overturning would only be 
reached when the direction of the resultant pressure passed 
through the outer edge of the wall. 

2d. That the moment of weight of the wall with respect 
to an axis passing through the centre of pressure shall be at 
least equal to or greater than the moment of the outside press- 
ure on the wall in respect to the same. This axis is taken as 
passing through the centre of pressure rather than through or 
along the outer edge of the masonry, for reasons of safety, as 
above stated, as the effect is to reduce the actual moment of 
the weight and to increase the moment of pressure. 

101. This subject has been theorized and experimented on 
perhaps as much as any other engineering problem except that 
of arches. Formulae are conflicting, owing to the uncertainty 
and variety of conditions actually existing. Many are the 
results of miniature experiments. Mr. Rankine evolves a for- 
mula purely from theoretical or supposed conditions, — all, no 
doubt, approximating the truth. 

102. The requisite thickness of the wall is a certain fraction 
of the height. The practical result, however, obtained is that 
at any point of ,the wall, from the top to the bottom, the 
thickness of the wall must be not less than one third of the 
vertical height from the surface of the ground to that point, and 



54 A PRACTICAL TREATISE ON FOUNDATIONS. 

need not in general be more than one half the height. Two 
fifths of the height may generally be taken as a safe thickness,, 
all depending upon the nature of the material resting against the 
wall. If this material is in the nature of a fluid, such as water, 
quicksand, and the like, a greater thickness may be required — 
even equal to the height. If there is danger of the material 
being converted into a flowing mass by the presence of water, 
a good plan is to place a vertical (or nearly so) layer of broken- 
stone or gravel between the material and the wall. This will 
serve to carry off the water, small holes being left through the 
wall to allow the water to escape. Retaining-walls sometimes 
bulge outwards without sliding on the foundation-bed or over- 
turning. When such is the case the wall may be considered 
in a precarious condition, but new relations between the press- 
ures arising therefrom may result in a condition of stability,, 
and the wall may remain in its then condition for a long time. 

103. The face of a retaining-wall is generally built of rough 
ashlar masonry, may be built of block-in-course or of brick, 
for two reasons: 1st. The main pressure is concentrated 
towards the face of the wall, and a better class of masonry is 
required. 2d. For the sake Of appearances. The back of the 
wall is generally of a rough rubble, composed of large and 
small stones. The face and back should be thoroughly tied 
or bonded together, so that the entire wall may act together 
in resisting the pressure. The face of the wall is generally 
built on a batter, as in piers, but the back is almost always 
built in a series of steps of greater or less rise. This increases 
the stability of the wall, by bonding into the material behind, 
and having its weight increased by the weight of the natural 
material resting upon it. Some additional stability can be 
secured by inclining the wall backwards towards the pressure, 
or the same stability by this method can be secured with less 
masonry. 

104. The face of the wall is built, as in case of piers, rest- 
ing on the usual footing-courses, both to spread the pressure 
over a larger surface, and at the same time to throw the centre 
of pressure further inward from the face of the wall. 



RE TA INING- WALLS. 55 

105. When a retaining-wall is in the nature of a railroad 
abutment, or the abutment pier of arches, supporting a narrow- 
embankment with the ordinary slopes, which generally are at 
the rate of \\ feet horizontal to each foot of vertical height, 
it is necessary to build at each end wing walls constructed as 
the face wall of the abutment, that is, with ashlar face and 
rubble backing. These wings can be built in the prolongation 
of the face wall, but decreasing in height, generally by a series 
of steps, as the slope of the bank descends ; the total length of 
this wing at bottom would then be equal to i£ times the total 
height, the object being, by following with the masonry the 
slope of the embankment, to prevent the earth from falling in 
front of the abutment. Sometimes the wings run to the front 
and perpendicular to the main walls for a length determined 
by the circumstances of the case. This plan is rarely used, 
except in coming out of a tunnel, to support the sides of the 
open excavation ; it of course adds immensely to the stability 
of a wall. Or the wings may extend, in case of an embankment, 
perpendicularly to the rear for a distance equal to from I to 1^ 
times the horizontal base of the slop.e More commonly the 
wings make an obtuse angle with the face of the wall, depend- 
ing upon the circumstances of the case. This plan is spe- 
cially applicable to abutments on the banks of watercourses, 
where from the direction of the current there would be danger 
in time's of floods of the water getting behind the abutments 
and scouring out the embankment. The angle between the 
main wall and the wing walls depending on the angle between 
the current of the stream and the direction of the embankment, 
and even when the directions of the stream and the embankment 
are at right angles, it has the advantage of presenting a funnel- 
shaped entrance and exit for the water, thereby relieving the 
danger of obstructing the free flow of the stream. The wings 
adding considerable stability to the main walls, these may not 
be as thick as required in isolated walls, resulting in a small 
saving of masonry on each abutment ; and on a long line of 
road a little saved here and there amounts to an important 
item of cost. Main and wing walls should be finished with 



$6 A PRACTICAL TREATISE ON FOUNDATIONS. 

good large coping-stones, but these need not be cut or dressed 
as neatly as is the custom on piers. 

106. In designing retaining-walls for the abutments of a 
bridge the steps on the back are so arranged that on the top of 
any step the thickness of the wall should be from i to ^ the 
height from the surface to that point ; this is then carried up 
vertically for a certain distance, then another step is made, and 
so on. The back of the wall may be as rough as the builder 
pleases, provided the minimum thickness is maintained, and to 
avoid unnecessary care the builder always makes it thicker than 
required. On the front a bridge seat of from 3 to 5 feet in width 
must be provided for the end rest of the bridge, and back of this 
a wall, called a breast wall, must be built up to the under side of 
the crossties on the bridge ; this is made from 2 to 2-| feet thick 
and from 2 to 4 feet high, depending upon the length of the 
span and form of truss used, this information is obtained from 
the bridge company. The bottom dimensions are determined 
from this data, as in case of piers. In very high walls the 
centre of pressure on the foundation may vary materially from 
the centre of figure of the base, and care must be taken to 
keep it within the limits above prescribed in order to avoid too 
great unit of pressure on the base ; this can be done by spread- 
ing the base with concrete and offset course. 

107. In order to prevent any tendency to slide, the condi- 
tion of frictional stability must be fulfilled, which is that the 
direction of the resultant pressure must not make with the 
normal to any horizontal plane from bottom to top an angle 
greater than the angle of repose, — that is, than the angle at 
which the upper portion would slide on the lower. There is 
practically no danger of the sliding of one course of masonry 
on another, but the wall may slide as a whole upon its base ; 
but in either event this tendency can be prevented by inclining 
the plane of the bed-joints so as to be nearly perpendicular to 
the direction of the resultant pressure, or the foundation bed 
can be cut into the form of steps. Good judgment can alone 
determine when these things are necessary. Cases have arisen 
when it was necessary to anchor the wall by the use of long 



RETAINING- WALLS. 57 

-rods passing through the wall and fastened to iron plates or 
timber walls embedded in the ground some distance behind the 
wall, or by inclined struts in front resting at one end against 
the wall, and the other against walls embedded in the ground 
in front. These rods or struts should generally rest against the 
wall as near the bottom as convenient, — theoretically at a point 
•§■ of the height from the bottom. 

108. The piers of a bridge on the Warrior River in Alabama 
built on and too near the sloping banks, without driving piles 
for them to rest on, had to be held in position by a system of 
strong struts as described above ; and pneumatic tubes were 
sunk in an inclined position in front of the abutment piers of 
a bridge across the Schuylkill River in Philadelphia to prevent 
a continuation of a sliding discovered after completion of the 
bridge ; and other instances could be cited, but withal it is 
rarely required. 

In very high abutments large archways are often left under 
the wing walls, extending backward, for roadways as well as for 
^economy. 

Article XI. 

1/ 

FORMULAE FOR THICKNESS. 

109. The various theories and resulting formulae seem 
either to be based on uncertain or erroneous data, and without 
undertaking to discuss or criticise these the writer will content 
himself with giving the geometrical representations of the 
■conditions of stability and the common formulae based upon 
the supposed conditions. Mr. Rankine assumes that the direc- 
tion of the pressure is parallel to the surface of the ground, 
that its intensity is uniformly varying, and that its amount is 
represented by a prism whose base is a triangle, sab, Fig. 4, 
and whose length is the length of the wall. The triangular base 
is constructed as follows : From a, the bottom of the wall, draw 

,ab = x -r parallel to the surface of the ground and also draw 

the line sb ; then area of triangle sab = \ab X sc x = also to vol- 



58 



A PRACTICAL TREATISE ON FOUNDATIONS. 




Fig. 4.— Cross-section op Retaining- wall. Prism of Earth Pressure. 

Earth Pressure. 



Resultant of 



EO 

6: 
&>: 

sab ■■ 



ab 



- surface of ground ; 

: angle of slope of ground; 

" " repose ; 
area of base of earth prism { 
: x = vertical side of sab) 
■■ x cos 6 = altitude of " 

px cos — i/cos 2 — COS 2 

: X — = X- 
P 



cos 0+|/ C os 2 e — COS 2 </>' 
: pressure of the earth = Uu ; . 
: weight of wall = tiiv ; 
: thickness of wall = Aa ; 
centre of gravity of triangle sab; 
: " " " " wall; 
: resultant pressure ; 
r — centre of " 
g y W = line of action of weight of wall ; 
ri = qt = generally \t; 
ki = q^t may be -(- or — ; 
ha — \x\ kai = ±x cos G; *-,<7, = ay — (qt-\-\t) sin 9- 



P: 

W: 
t: 

g z 
g> ■■ 



RETAINING- WALLS. 59> 

ume of earth prism unity in length ; and if w' = weight of unit 

of volume of earth, weight of prism = P = . Mo- 

. , , „ w'iab X sc) 
mentof pressure of earth = Px vr — — - X {Jia, — r^a,)^ 

Substituting values given above, we have, for the moment of 
the pressure tending to overturn the wall, 

„ w'x 1 cos 9 p t 
PX vr= x ~X (i^cos 0-(g + $)t sin 9). (i) 

2 p 

The moment of resistance to overturning will be the weight 
of the wall -f- the weight of earth resting on the steps (= W\ 
multiplied by its lever arm (= rk) = W.rk = W{ri ± &i) = 
W{qt ± qj)q x t. The quantity qj will be positive or negative 
as the line of action of the weight g x W is on the opposite or 
the same side of the centre of figure of the base Aa ; in the 
Fig. I above it is negative. The moment of stability is thus 
M= W(qt ± qj), and this must be equal to or greater than 
the moment of the external pressure ^X^; q being generally 
assumed = f . 

iv' ' x* cos 9 , h 

m±q>)t> ; — x & x {\x cos e-te+w sin &). ( 2 > 



The condition to resist sliding or stability of friction is that 
the angle rt x k < <p, the angle of repose of masonry on masonry, 
varying from 25 to 30 . Generally, all the quantities in 
eq. 2 are given except t, which can then be found. <f> can be 
measured or calculated. In Fig. 1, 

0,0, = {o,w, -f t x w,) X tang oJ,o ; 

o t o, = P cos 9 ; o,w = P sin 9 ; t % w 9 = W\, 



:. we have 



Pcos 9 
rang of/,, = W+Psin e < tang 



60 A PRACTICAL TREATISE ON FOUNDATIONS. 

as the condition of frictional stability. For fluid pressure 

P 
6 = cos 6 = i ; sin 6 = 0; — = I. 



P 



Eq. 2 then becomes 

Wx 



Mi ± &¥>-£-, (3) 



and 



-^>= tang oJ x o x < tang <p (4) 

This whole theory from beginning to end is beautiful, and 
if the premises are true the conclusions are also. It is analo- 
gous to the pressure of water, and the formula is easily appli- 
cable to the pressure of water by making both 6 and 0' equal 
to 0, the formula then becomes 



m+9)* 



as 



1\ + 


W X W X 


q)t 


- 2 ~ * 6 ' 


A 


cos 6 — l/cos 2 6 — cos a 0' 


P 


cos -f- |/cos 2 6^ — cos 2 0' 



in this case. A practical example will be given in a subsequent 
paragraph. 

HO. The only other formula that will be mentioned may 
be called Moseley's. This is based upon the following condi- 
tions, namely, when a mass of earth is allowed to assume its 
own slope it will generally slide down until the slope makes an 
angle with the horizontal equal to the angle of repose, then it 
will have its natural slope ; but if a wall with a vertical face be 
built to prevent this sliding, a pressure will be exerted against 
the wall by the tendency to slide. Experiment or theory or 
both show, however, that the weight of this sliding mass does 
not represent the maximum pressure, but if a plane be taken 
bisecting the angle between the natural slope and the back of 



RE TA WING- WA LLS. 6 1 

the wall, the prism nearest the wall will exert the maximum pres- 
sure. The direction of the pressure is taken to be horizontal, 
and the point of application of the resultant pressure on the back 
of the wall will be at \ of the height of the wall from the bot- 
tom. Let AB (Fig. 5) be the back of the wall and vertical, BC 
the natural slope ; then BD bisecting the angle AB {Twill be the 
plane of rupture, and the prism ABD will produce the maxi- 
mum pressure. Hence, considering the length of the wall 
unity, the area ABD will also be the volume. Area ABD 

AB X AD x* tang ABD -, .,„«,, 

= = , and the weight W of the prism 

w'x* tang ABD , , , , . . n 

equal to ■ — ■ , and the pressure due to this is P 

w'x* tang* ABD TTT , „„r^ 

= = W tang ABD, and the condition of sta- 

2 & 

bility will be, as before, 

wV tang 3 ABD w'x* tang 2 ABD 
W(%±q 1 )t = f Xi* = £ . (5) 



in which W equal to the weight of wall and earth on the steps 

(assuming a plane of division along AB), to be determined from 

the cross-section of the wall ; small w' = unit weight (1 cu. ft.) 

of the material supported by the wall ; t = FB = thickness of 

qo° — angle of repose ((p) 
wall, and angle ABD = " - ^- ; . The lever 

arm of the external pressure = \x = hB ; AB = x = height of 
wall. The moment of stability = W{qt ± qj), and the condition 

P 

of frictional stability tang vrt x = rtjz = tt? < tang <p. 

III. Both of these formulae are supposed to be based on 
erroneous or false assumptions, and consequently the results 
are not considered at all reliable. They are, however, approxi- 
mately true if the material is clean sand. As a simple applica- 
tion of the formulae and for the sake of comparison, we will 
assume the following quantities : AB = x = 20 ft. height of the 
wall, supporting clay in a fair or normal condition, surface AC 



€2 



A PRACTICAL TREATISE ON FOUNDATIONS. 



-of earth horizontal. The wall of rectangular horizontal section 
and vertical section, BC the natural slope, BD the plane of 
rupture, the angle of repose = CBH = 34 ; then ABB = 

- — ~ = 28 , and tang 28 = 0.53. The line of action of the 

weight passing through the centre of gravity of the base, or 
rather centre of figure, hence q x = o; weight of a cubic foot of 




Fig. 5.— Cross-section of Retaining-wall Prism of Maximum Pressuhj Resultant. 



clay = w = 120 lbs., and w = weight of a cu. ft. of masonry 
= 15.0 lbs. W = wxt — 150 X 20 X t. Substituting these 
values in eq. 5, par. no, W(% -f- q)t — \w'x % tang 4 ABB, we 
have 150 X 20 X t X f * = \ X 120 X 8000 X 0.2809 ; hence t = 
6.3 ft. = thickness of wall. Now substituting in eq. 2 (Rankine's), 

w'x 1 cos 6 t> 
m + ?,)' = 2 Xj X for cos 6- (? + £)* sin 0, 

recollecting that 



/, cos — rcos' — cos* <p' 1 — sin 0' 

p ~~ cos -f- ^cos* — cos 2 0' = 1 + sin 0" 



RETAINING- WALLS. 63 

since = o ; cos = i. And sin 6 = o, also the sin <j>' = sin 
34° = 0.56; 

9 = 1 ^ = 0.28. 

p 1 + .56 

Substituting, 

120 X 400 X 0.28 
150 X 20 X t X \t = ~ X i X 20, or t = 6.3 ft. 

The formulae reducing to the same value under these conditions, 
and as the angle of repose assumed is about that for dry sand, 
the formulae give fairly good results. The least thickness in 
practice would be 1 of 20 = 6.6 ft., and more generally would 
be f of 20 = 8.0 ft. For wet clay or quicksand the formulae 
give about 9.0 ft., but in practice it should not be less than 15 
to 18 ft. These formulae will generally give a less thickness 
than would be good practice. It will be observed that the 
axis about which moments have been taken is at a point % of 
the thickness of the wall from the outer edge. If it had been 
taken at the outer edge the moment to resist overturning 
would have been a little greater, and consequently the result- 
ing thickness would have been a little less than those obtained. 
In applying Rankine's formula for fluid pressure the only 
changes necessary would be in the value w' from 120 lbs. to 
62\ lbs. per cubic foot, and in making <p' and 6 = 0; then sin 

A 

== sin 6 = o, and — would become unity. The substitu- 

tion would give 

62.5 X 400 

150 x 20 x t x \t = — — 2 X i X 20. 

t — 8.6 (should be 10 ft.) thickness of wall for water pressure. 
Water pressure can be calculated easily in any case by multi- 
plying the area of the immersed surface by the depth to which 
its centre of gravity is immersed and by the weight of a cubic 
foot of water (= 62% lbs). The point of application of resultant 
pressure is one third of the height of the wall from the bottom. 
The direction of the pressure is always perpendicular to the 
surface pressed, and this is true whether the surface is vertical, 
inclined, or horizontal. 



64 A PRACTICAL TREATISE ON FOUNDATIONS. 

112. In the case of surcharged retaining-walls, from the tops 
of which the slopes of the embankments rise at the angles of 
repose, such as terraces supported by walls near the bottom, 
or in masonry walls surmounted by embankments, as in the 
case of forts, even theory seems to be silent on this subject. 
The only practical rule is to be sure to make them thick 
enough. In placing the earth behind retaining-walls the mate- 
rial should be placed in thin layers and well rammed for at 
least 10 ft. back from the wall ; it then may be dumped in the 
usual way. 

113. If the material is likely to become like quicksand or 
soft mud, it is best to assume it as a fluid having the weight of 
the solid material and the angle of repose equal to zero, as in 
case of water ; this will make the thickness from \\ to 2 times 
of that to support water. 

114. Retaining-walls are of three kinds. Where the wings 
are inclined to the face of the wall, they are simply called wing 
abutments ; where they extend back perpendicularly, with a 
hollow space between, they are called " U " abutments, the 
hollow to be filled with earth ; and where a solid stem extends 
back, they are called " T " abutments. There is no advantage in 
the last, and requires more masonry, as a rule. The T abut- 
ments should be left hollow for about 2 ft. from the top, so as 
to allow sand, clay, or broken stone to be used for the cross- 
ties to rest on, as otherwise a jarring disagreeable motion will 
follow when a heavy rolling load passes. 



Article XII. 

ARCHES. 

115. THE theory of arches is perhaps as little understood 
as in ages past. Some fall, some are doubtless in a precarious 
condition, some stand. Mathematical and mechanical theories, 
after carrying you through the intricate mazes of higher 
mathematics, have surely led to no satisfactory or practical 
results. The theory of graphics is more pleasant to handle, 



ARCHES. 65 

certainly easier to grasp, and may do admirably to back up 
guesses, or to shift responsibility in case of accident or failure. 
Mr. Rankine, after going through a most able and wonderfully 
conceived discussion of this subject, tells you to make your 
factor-of-safety from 20 to 40, and closes by saying : " The best 
course in practice is to assume a depth for the key-stone ac- 
cording to an empirical rule, founded on dimensions of good 
existing examples of bridges." We might inquire here how the 
old arch-builders came anywhere near safe dimensions Did 
they understand the theory of the arch ? or did they arrive by 
repeated failures or disasters to what at any rate are safe 
dimensions, and we now profit by their experience ? We must 
do the best we can, but be sure of being on the safe side. 

116. Having fixed upon the depth of the key-stone, the 
same depth is maintained down to the springing line, in small 
arches. In arches of long span the depth increases gradually 
from crown to springing line, so as to maintain the unit pressure 
the same throughout, according to a simple and well-known law, 
that at any bed-joint the resultant pressure will be the hypo- 
thenuse of a right-angled triangle, of which the base is taken 
to represent the horizontal thrust at the crown and the altitude 
the weight on that portion of the arch ring from the crown to 
the bed-joint under consideration ; and by proper construction 
to scale on the drawing itself, the direction of the resultant and 
centre of pressure can be determined. At the springing the 
resultant pressure is represented in direction, magnitude, and 
point of application, which three elements must be known, by 
the hypothenuse of a right-angled triangle, the base being the 
horizontal thrust at the crown, the vertical being the weight of 
the half arch and any load upon it, supposed to pass through 
the centre of gravity of the mass. Following the process 
above mentioned for finding the centre of pressure at each bed- 
joint in the arch ring, the line passing through these centres of 
pressure is called the line of pressure, which for safety should 
be confined to the middle third of the thickness of the arch 
ring. Although after all this we may be in doubt whether the 
line of pressure will under all conditions remain where we put 



66 A PRACTICAL TREATISE ON FOUNDATIONS. 

it, yet we fortunately do know by experiment and observation 
the manner in which both flat and pointed arches give way ; 
and though we may have blundered in determining the 
thickness of the arch ring and the proper curve to which it 
should be built, the above knowledge enables us to correct this 
error by what is known as the backing. Flat arches give way 
by breaking into four parts, — opening at the crown of the arch 
on. the underside or the intrados, and opening on either side at 
a joint not definitely known, on the top or extrados, but never 
above that point which makes an angle of 45 with the horizon, ' 
the two upper parts falling inwards and pressing the two lower 
parts outwards. This last can be prevented by carrying up the 
masonry of the abutments above the point mentioned, and this 
in turn preventing the upper parts from falling. 

117. In pointed arches the condition is just reversed, the 
two lower parts falling inwards and tending to lift the upper 
parts. This can be prevented by weight of sufficient magnitude 
on top ; so, notwithstanding the ignorance on the subject of 
arches, by due precaution we can feel reasonably safe as re- 
gards the stability of any given arch. 

118. The almost universal rule is to build the ring of the 
arch of the very best kind of ashlar masonry, cut so that the ring 
stones may bear against each other with the thinnest possible 
joints, which can be filled with grout or at least very thin mor- 
tar. The backing, the abutments, and the spandrels, or the 
wall resting on the arch ring, can be built of a less costly class 
of masonry. 

119. Applying the principles explained in discussing retain- 
ing-walls, the direction of the pressure is towards the back of 
the wall rather than the face ; hence the back of an abutment 
carrying an arch should be built of ashlar, or at least a good 
class of masonry. The exposed face need not be so good, but 
for appearance' sake it is generally ashlar ; but in the case of 
arches the abutment is generally supported on the back by an 
embankment, and the same care is not necessary in building 
the back or unexposed face of the masonry. 

120. In building an arch ring it should be built from both 



ARCHES. 67 

abutments at the same time upwards towards the crown, con- 
sequently the arch ring has to be supported until the arch is 
completed, that is, when the key-stone is put in. The frame- 
work, generally of timber, which supports the arch ring is called 
a " Centre ;" this centre generally remains in place until the 
cement has had time to set, and is then removed. The frame 
generally rests on wedges ; these being driven out gradually, the 
centre falls from the arch without shock or jarring. 

121. Arches are generally built over streams, roads, open- 
ings such as doors and windows in houses ; and sometimes where 
large, heavy masses of masonry, such as unusually large piers or 
abutments, are to be built, requiring large quantities of masonry, 
the amount of masonry can be materially diminished by the 
use of arches, without injuring the stability of the structure. 
Where the stone of which it is built is strong and hard enough 
to bear the superincumbent weight on a considerably reduced 
area of bearing surface, and where also the foundation bed can 
bear the increased unit pressure, this can be reduced by the 
use of inverted arches under the arch proper. Stone arches of 
great span are not now built to the same extent as they were 
formerly, iron and steel having been substituted to a very great 
extent, and generally as horizontal trusses. 

122. With no exact mathematical formulae to guide us in 
the construction of arches, we are mainly compelled to follow 
some empirical rule, based upon the dimensions of existing 
arches, which at least stand though we do not know the 
amount or direction of action of the external forces or loads, 
even when fixed or dead, and still less of the effect of heavy 
rolling or moving loads. We can, however, approximate to 
these ; and with the knowledge that the arch ring must give way 
either by crushing the voussoirs or arch stones, or by the slid- 
ing of one stone on another, or by the arch ring rotating or 
revolving inwards or outwards around the inner or outer edges 
of some of the stone as an axis, we can arrive at a safe thick- 
ness of the arch ring and the proper form of the arch ; and 
in general we boldly assume the form of the arch ring and the 



68 A PRACTICAL TREATISE ON FOUNDATIONS. 

thickness of it, and by a tentative process determine whether it 
will be stable under the conditions assumed. 

We know the resistance to crushing of the stone, — this must 
not be exceeded by the greatest pressure to which it is subjected 
after allowing a large factor for safety, — and that it should be 
distributed as uniformly over the bearing surface of the stone as 
possible, and for this the centre of pressure should be as near the 
centre of the bearing surface as possible. To resist overturning 
around the edge of any jointthe centre of pressure must not be 
above or below the arch ring at any point, but must be on the 
surface of the stone, and as near the centre of figure as possible — 
at any rate within the middle third of the arch ring. To prevent 
sliding, the resultant pressure at any bed-joint must not make 
an angle greater than the angle of repose with the normal to 
the bed-joint at that point. The backing should be built up 
above that joint which makes an angle of 45 with the vertical ; 
this backing is generally carried up to the crown, gradually 
thinning as it approaches the top. All of these conditions be- 
ing fulfilled, the engineer may feel reasonably safe as to the 
stability of an arch ; if, however, the graphical solution of the 
problem fails in any of the above respects, the arch ring must 
be made thicker or the form of the curve changed, or both. 

123. It will be best to define the terms that will be used. 
The arch, taken as a whole, consists, 1st, of the abutments 
from which the arch springs ; the top of the abutment on the 
inner edge is called the springing line ; the truncated wedge- 
shaped stones resting on the abutment are called Skew-backs ; 
2d, of the arch ring itself, composed of wedge-shaped stones, 
called voussoirs or ring-stones, of varying sizes, but for the same 
arch the breadth should be as uniform as practicable; lengths 
should vary in order to get bond; the' under side of the stones 
are cut to the curve of the arch. The under or cylindrical sur- 
face of the arch is called the Intrados or Soffit. The upper 
surface or back of the stones (generally left rough, conforming 
roughly to the curve of the ring of the arch) is the Extrados or 
back. The thickness of the ring is determined by the depth 
of the surfaces in actual contact included between two parallel 



ARCHES. 69 

curves, the intrados and extrados proper. The exposed under 
surface is generally dressed smooth ; the joints between the 
voussoirs are always cut true. The bed-joints or surfaces of 
contact of the stones radiate from the centre or centres of the 
curves of the arch ring. The Key-stone is at the top of the 
arch or crown ; it is the last stone put in, and the arch is not 
self-supporting until it is in place. The face of the arch is its 
■end or head, the axis is the centre line, perpendicular to 
the head of the arch in square arches, and oblique in Skew 
arches. A ring-course is a portion of the arch ring included 
between two vertical planes perpendicular to the axis or par- 
rallel to the head of the arch, and at any distance from each 
other, — say a foot or two. A String-course is that portion of the 
arch ring included between two inclined planes extended from 
end to end of the arch and intersecting in the axis of the arch, 
these planes containing the contiguous joints between the 
stones. The centres of pressure are the points in which the re- 
sultant pressures pierce the joints between the stones, and the 
line of pressure is the curved line passing through them. In 
large arches, especially when flat, the thickness of the ring- 
stone increases from the crown to the springing as the secant 
of the angle of inclination of the curve at any point, and at the 
springing maybe 1^ times that at the crown ; in circular arches, 
if small, no increase is made generally. 

124. A Full centre arch is a semicircumference in cross-sec- 
tion, and is rarely used except for comparatively small arches, 
as the rise would be too great, if for no other reason. The 
Segmental arch is flat, and generally a segment of one circle, with 
a long radius, and is called a one-centre arch ; sometimes it is 
composed of segments of three circles, the upper part of a long 
radius, and the portions near the springing, called the Haunches, 
having short and equal radii: this approaches the elliptical form, 
and is generally called the elliptical arch ; the true ellipse may 
be used. The span of the arch is the horizontal distance from 
the springing line to springing line. The Rise of the arch is 
the vertical distance from the springing line to the soffit at the 
crown. 



/"O A PRACTICAL TREATISE ON FOUNDATIONS. 

125. The Spandrel Wall or parapet wall is not an essential 
part of the arch, but is built to give a finish to the ends, and at 
the same time if an embankment is built over the arch it serves 
as a retaining-wall for the foot of the slope of the embankment. 
It is a wall 3 or 4 feet high, built over the ends of the arch ring 
and in the plane of the arch, and is finished with a coping ; it, 
with the wings, prevents the earth from rolling over or around 
the ends of the arch ; it supports a surcharge embankment and 
should be thicker than that of a retaining-wall of that height. 
Sometimes intermediate walls are built parallel to the head 
walls. The backing between the head walls is really a part of 
the arch proper. 

126. To determine the length of an arch, from end to end 
supporting an embankment above, the slope of the embankment 
being 1^ to 1, it is merely necessary to deduct from the width 
of the embankment at the bottom three times the height from 
the ground line to the top of the spandrel wall ; the arch should 
be a little longer than this difference. The wing walls then 
extend to the foot of the slope. 

127. The masonry of the abutment is generally faced with 
ashlar, block-in-course, or coursed rubble masonry ; theoreti- 
cally, the back should be equally good or better than the face, 
but is generally of a rougher finish. Owing to the fact that the 
thrust of the arch tends to overturn the wall in one direction 
and the embankment in the other, the direction of the result- 
ant may be inclined either way, or may be vertical according 
to their relative magnitudes. The embankment should be built 
on both sides of the arch at the same time, and should be 
rammed in layers around and over the arch for at least 10 feet 
in thickness, after which the earth may be dumped in the 
usual way. It is customary to pile up. behind the abutments 
the shivers of rock and debris accumulating around the work. 
This facilitates the drainage, and at the same time strengthens 
the wall until the embankment is built. 

128. In small arches, unless the bed of the stream is rocky, 
it is best to pave the bottom between the walls with stone 
from 6 to 12 inches thick, and also to build apron walls under 



ARCHES. J I 

the ends deeper than the foundation bed of the abutments, to 
avoid any danger of scouring. The spans for such arches gen- 
erally vary from 5 to 20 feet, and are generally full-centre 
arches. For longer spans it will generally be economical to 
use the flat or segment arch, and avoid too great a rise of the 
arch. 

129. The arch ring-stones are all dressed true on the joints 
and soffit, and are of best kind of ashlar. The width of the ring- 
stones is seldom less than one foot or more than three feet, and 
the thickness or depth from one to five feet. The upper sur- 
face is, in general, covered with a layer of cement or asphalt, 
or some waterproof substance to drain the water to the proper 
drains, and prevent the dripping that would otherwise pass 
through the joints of the ring. The stones of the arch ring- 
break joints in the direction of the length of the arch. Arch 
stones are often cut and marked so as to fit in a certain posi- 
tion, as shown on the development of the arch on paper ; this 
is convenient, and saves time and trouble. The development 
of a square arch would be a rectangle, one side of which is the 
length of the arch, and the other side is the length of the arch 
ring itself, upon which the string-courses can be laid down to 
scale in their true positions, and arranged so as to secure the 
proper bond, and the arch ring should be built to correspond. 
The ring-coursed stone on the ends of the arch are cut on top 
to vertical and horizontal surfaces in order to let the spandrel 
wall rest true on the ring, and also to bond with it, also for 
appearances. 

130. The masonry of the spandrel may be ashlar or block- 
in-course masonry, backed with rubble. The wings may be the 
same kind of masonry, and proportioned as in retaining-walls. 
The backing is generally of heavy rubble or may be made of 
concrete, rounding off towards the crown of the arch, and cov- 
ered over with a layer of cement. 



72 A PRACTICAL TREATISE ON FOUNDATIONS. 

Art. XIII. 

SKEW ARCHES. 

131. THE skew arch is built of the same parts and of the 
same kind of masonry in the corresponding parts, but, owing 
to the inclination of the axis of the arch to the plane of the 
face, the string-course joints are curved, and each joint is of a 
different kind of curve — that is, a series of irregular spirals 
drawn perpendicular to the lines of pressure in different sec- 
tions of the length of the arch, taken at convenient intervals ; 
and, although the general conditions of stability are the same as 
in a square arch of the same span, the above directions of 
the bed-joints require every stone in the arch to be of a 
different size and shape, with all surfaces curved. Here the 
knowledge of descriptive geometry and stereotomy are re- 
quired to determine the shape of the stone, and to construct 
the templets to guide the stone-cutters. This is troublesome 
and laborious, and requires great accuracy and care, as each 
stone will fit in but one position in the arch ring ; the cutting 
is expensive, the building is troublesome and slow, the whole 
structure is costly; hence engineers avoid as much as possible 
the use of this arch, and have so modified its construction as 
to avoid these difficulties. 

132. Only a general outline of the first method will be 
given, the method of constructing the development of the 
soffit will be found in Rankine's Civil Engineering, pages 450 
and 451. 

133. The first thing is to draw to a large scale the develop- 
ment of the soffit of the arch. A ring or wheel when revolved 
once develops a straight line, equal in length to the circum- 
ference of the wheel ; a right cylinder, or take a semi-cylinder, 
when revolved develops a rectangle, the length of which is the 
length of the arch, and the breadth is the length of the semi- 
circumference on the soffit of an arch ; and an oblique cylin- 
der, or the skew arch, when revolved will develop a figure ap- 



ARCHES. 73 

proaching the rectangular in shape, with two straight parallel 
sides equal in length to the length of the arch, the other 
sides parallel, but curved, and equal to the length of the 
soffit. 

134. A full discussion of arches, development of the soffit, 
lines of pressure, ring and string course joints, thrust or pres- 
sure at the crown and at other points, etc., will be found in 
another volume. 



Article XIV. 
DEPTH OF KEYSTONE. 

135- There are many methods and theories on this 
subject, but as none of them lead to better or more certain 
or more reliable results, the reader is referred, for full dis- 
cussions, to such authors as Rankine, Weisbach, Moseley. In 
practice empirical formulae are used. Trautwine gives the 
following practical formula for determining depth of arch 
ring at the crown : Depth of key-stone in feet equal to 

( V radius -f- £ span\ ,,',,., , 

I ) -j- 0.2 ft. for first-class cut-stone work. 

Increase this result by -§• part for second-class work, and for 
brick or rubble \ part. The depth of the arch ring should in- 
►crease, theoretically, from the crown to the springing, this 
increase at the springing being from one-fourth to one-half the 
depth at the crown, but is never necessary for small arches. 
Rankine's formula is : Depth of key-stone in feet equal to 
|/o.i2 X radius at crown ; and for an arch of a series the depth 
of key-stone in feet equal to Vo.ij X radius at crown. For 
tunnels, which generally have elliptical cross-sections, depth of 



key-stone in feet equal to Vo.\2r, in which r = -r, in which a 

is the rise of the arch from two thirds to three fourths of the 
transverse diameter and b is the semi-conjugate diameter. 



74 A PRACTICAL TREATISE ON FOUNDATION'S. 

In soft and slippery materials the thickness should be doubled. 
Assuming a radius at the crown of 160 ft. and span 147.6 ft., 
Trautwine's formula gives depth of key-stone equal to 4.0 ft. 
and Rankine's 4.4 ft.; actual thickness 4.9 ft. This was a 
segmental arch. Again, by Rankine, an elliptical arch 30 ft. 
span, and rise "j\ ft., calculated thickness 1.9 and actual thick- 
ness 2 feet; a 90-ft. span segmental arch, rise 30 ft., calculated 
thickness 2.88, actual thickness of key-stone 30 ft. About the 
largest arch built is the Cabin John aqueduct, Washington, D. C. 
Span 220 ft., rise 57.25 ft., radius at crown 134.25 ft., thickness 
of arch ring at the crown 4.16 ft., and at the springing 6.0 ft. ; 
segmental in form. For depth of this arch at crown Traut- 
wine's formula gives 4.1 ft., and Rankine's 4.0 ft. Therefore 
we may safely conclude that either formula gives safe results 
in practice. 

136. To what extent and in what manner a heavy rolling 
load affects the line of pressure or the stability of an arch is 
not known, but in very large and heavy arches, or where there 
is a great depth of earth over the top, it probably causes no 
great change. Several feet of earth or ballast should be placed 
over an arch to prevent the effects of shocks from a rapidly 
moving train. Arches are built of masonry, iron, or wood ; the 
same general principles are applicable. 

The above conditions are necessary to prevent overturning 
around the edge of any joint. To prevent sliding at any joint, 
the direction of the resultant pressure must not make with 
normal to that joint a greater angle than the angle of repose 
or of friction of stone on stone ; this is not likely to take place 
unless the abutment settles. 

137. In the above considerations no account is taken of the 
tenacity of the mortar or its adherence to the stone, which 
would add materially to the strength of the arch. 

138. The conditions of stability of the abutment is the same 
as that of a retaining-wall acted upon by a resultant pressure 
equal in magnitude, direction and point of application of the 
resultant pressure of the arch at the springing. By building 
the abutments in courses radiating from the centre of the arch. 



BRICK. 75 

the line of pressure in the abutment would be a continuation 
of the line of pressure in the arch ring, this should be confined 
in the middle third of the abutment, and when the courses 
are horizontal is an approximate continuation of that line. 
The flatter the arch the greater will be the tendency to over- 
turn the abutments. 



Article XV. 

BRICK. 

139. Brick Walls and Piers — Stone is always preferred for 
large piers and abutments, but in many parts of the country, 
especially in many Southern States, brick has to be relied upon 
for almost all purposes ; and in all parts of the country brick is 
very largely used for private dwellings as well as for many 
public buildings. Brick can be called- an artificial stone. The 
principal ingredients in brick are clay, sand, protoxide of iron. 
Other substances that may enter into ordinary clay either do 
no good or are absolutely harmful, carbonate of lime in any 
large proportions rendering the clay absolutely unfit for making 
brick. Sand should not exist in any excessive quantity. Protox- 
ide of iron causes the red color in brick after burning, and also 
increases the strength and hardness. 

140. In making brick the clay is reduced to a state of rather 
stiff mud with water, then placed in what is called a " pug-mill, '* 
which consists essentially of a vertical cylinder, in the centre 
of which is a vertical shaft with radiating arms, so shaped and 
fixed that on turning the shaft, generally by a horse hitched to 
the end of a lever, the clay is thoroughly kneaded, and at the 
same time forced downwards to the bottom of the mill, where 
it is passed out of an aperture on to a platform, where it is then 
pressed into a mould of suitable size and shape. It is then 
placed on an open, well-prepared yard, where it is sun-dried for 
a short time. When properly dried (it constitutes something- 
similar to the " adobe," which was formerly used for construct- 



76 A PRACTICAL TREATISE ON FOUNDATIONS. 

ing houses) the bricks are built in a large mass or kiln of a 
certain established width and height, and of a length depending 
upon the number of bricks, varying from 100,000 to 300,000; 
eyes or flues are left at the bottom as receptacles for fuel — in 
ordinary cases wood. The bricks are laid rather open, so as to 
create a draft and allow the heat to pass in and around them. 
When ready the fire is started slowly at first and increased 
to an intense heat, and after burning for a period determined 
partly by the fuel used, but mainly by experience, the fires are 
allowed to die out gradually. 

141. On opening a brick kiln after burning the quality of 
the brick may be divided into four classes, extreme outside 
brick, on sides and top being burnt so little that they may be 
thrown away as worthless ; then a layer inside of the above, of 
more or less thickness, in which the brick are under burnt and 
soft ; these are called pale or salmon brick, unfit for foundations 
or face work, but are used for filling in between good bricks in 
walls. In the centre of the mass forming the kiln a class of 
brick is found well burnt, hard, well shaped, and of good red 
color ; this class of brick is good for any purpose. The lower 
part of the kiln just above the eyes are over-burnt, very hard, 
very brittle, and generally distorted, cracked, and even vitrified; 
these are not suitable for structures exposed to shocks. The 
second class are called pale, salmon, or under-burnt brick, very 
soft and porous. The third, body or red brick, hard and 
strong and used in face of wall. 

142. Bricks are used for houses to a much larger extent 
than any other materials except wood. The walls of houses 
are generally carried up plumb or vertical, the dimensions at the 
bottom being determined by the nature and height of the walls, 
and purposes for which they are constructed, — warehouses, 
on account of the immense weight which may be placed on the 
floors, requiring thicker walls than dwelling-houses. This thick- 
ness in many cities is fixed by law, which doubtless corresponds 
with the practice very closely in all cities. The thickness is gen- 
erally stated as follows : 8-inch or 9-inch walls being one brick 
thick, 12 to 13 inches being \\ brick thick, and so on. Bricks 



BRICK. 



77 



vary a little in size in different parts of the country, but gener- 
ally in the following limits : between 8 and 9 inches long, 4 to 
4£ inches wide, 2\ to 3 inches thick. It will be noticed that 
the proportions of the several dimensions are about the same as 
for ashlar masonry. In ordinary houses, the thickness at the bot- 
tom varies, according to height, between 1^ bricks thick (say 
13 inches) to 4 bricks thick (32 inches), and decreasing to 1 
brick thick at the top for houses of moderate height, and i|- 
brick thick for very high houses. This decrease is not made as 
in piers by a regular batter, but by an abrupt changes or by 
offsets from story to story. The walls of warehouses should 
be thicker than the above, depending upon their size and the 
purpose for which they are used. The above dimensions refer 
to the body of the wall or the neat work ; the footing-courses 
about double the above. 

143. Brick-work is built in regular courses of the thickness 
of the brick, well bonded, and with joints of not over \ of an 
inch thick, or it is better controlled by saying that in a certain 
vertical height there shall not be more than so many courses 
of brick. If the brick is 2f inches thick, four courses should 
occupy a vertical foot on the face of the wall. 

144. There are two kinds of bond, the English and the 
Flemish. It is probably immaterial which is used ; but in the 
Flemish bond, where stretchers and headers alternate in each 
course, a more certain, uniform, and regular bond can be se- 
cured, a header being placed immediately over a stretcher 
below ; whereas in the English bond the headers are in separate 
courses, — one, two, or more courses of stretchers, then one of 
headers, this proportion being regulated by the character of 
the work ; a factory chimney, for instance, requiring a larger 
proportion of stretchers than headers, such as four courses of 
stretchers to one of headers. This kind of work should be 
rigidly executed, according to rules established both by theory 
and practice. More latitude can be given in the case of ordi- 
nary walls, but too much looseness and indifference is shown 
in this kind of work : so much so, that it is often impossible 
to say what proportion of stuetchers to headers is allowed, it 



78 A PRACTICAL TREATISE ON FOUNDATIONS. 

being practically left to the masons to decide. Mr. Ran- 
tine says one course of headers to two stretchers gives 
equal strength longitudinally and transversely in the English 
bond. 

145. Often in brick walls stone quoins or corner-stones are 
put in, these stones being, say, 10 or 12 inches thick, presumably 
to strengthen the corners, as well as for architectural effect; 
the policy in either case is at the best doubtful. 

146. A great difference of practice in building walls of 
houses exists in regard to filling the joints, and the common 
practice is to make good beds ; smear a dab of mortar on the 
end of the brick before placing it in position, leaving even the 
vertical joints of the stones unfilled, and no attempt being 
made to fill the back joints at all ; this practice certainly 
weakens the wall, even if it may have some compensating ad- 
vantages. 

147. The strength of ordinary bricks, such as the hard, red, 
well-burnt, is sufficient to resist crushing under any load that 
is likely to be placed on it in the walls of houses. This has 
been amply proved by experience in all parts of the country, 
and these bricks must have been made of clay varying largely 
in their composition, and both by hand and by many recently 
constructed machines. A few examples will suffice to establish 
the truth of the above. Mr. Rankine gives the actual existing 
pressure at the base of a chimney 450 feet high, 20,000 lbs. 
per square foot, or 140 lbs. per square inch. The brick shot- 
tower in Baltimore, 246 feet high, the pressure at the base is 
about 13,000 lbs. per square foot, or 90 lbs. per square inch, 
whereas i 100 lbs. per square inch is considered a fair ultimate 
strength for piers or walls of brick-work, giving a factor-of- 
safety of from 8 to 12. If good strong cement mortar is used, 
the ultimate strength can be taken at from 1 500 to 2000 lbs. 
per square inch ; the factor-of-safety will be at least from 1 1 
to 14. 

148. Brick piers and abutments are used to a large extent 
in the Southern States, on account of the difficulty and cost of 
securing stone of any kind. The writer built a bridge across 



BRICK. 79 

the Tombigbee River, on the line of the Mobile and Birming- 
ham Railway ; the piers were of brick, resting on concrete, in 
the cribs of pneumatic caissons, a little below the water sur- 
face, the pressure at the bottom of the brick piers about 
7600 lbs. per square foot of base ; the brick were almost en- 
tirely obtained by pulling down old and abandoned ware- 
houses in Mobile, Ala. The appearance of the brick indicated 
good strong brick, and the time that they had stood, with- 
out signs of wear or disintegration, indicated durability; in 
fact, they seemed to be superior to the new brick then being 
made. 

149. Good brick seem to be as durable as any ordinary 
stone, can be built at a less cost per cubic yard than stone, 
and resists the effect of intense heat, such as resulting from 
fires in cities ; is strong enough to carry any load likely to 
occur ; is not affected by acid atmospheres ; and now that 
brick can be obtained of different colors or variegated colors, it 
would seem that brick-work can satisfy all the conditions of 
strength, durability, and architectural effect desired. 

150. One cause of the apparent distrust in brick-work is 
that manufacturers of brick are too anxious to sell a poor 
quality of brick, made of poor material, under burnt and soft, 
often very irregular in shape and size ; angles not square, 
faces not parallel, and often badly warped and twisted. These 
defects, if confined to the backing or filling of the wall, would 
not be so objectionable ; but masons are too apt to use these 
on the faces of the walls, causing ugly joints, irregular courses, 
a general bad and rough appearance ; and in the filling they 
will use brick so soft that they are unfit for any purpose, and 
would soon return to the condition of mud if exposed. Often 
to get a sufficient quantity of brick you are compelled to 
take the general run of the kiln. These things cause a want 
of confidence. 

151. But the high walls of houses in addition to resisting 
crushing, have to resist also the tendency to overturn, either 
from external forces from within or without. There is little 
or no danger of overturning from external forces, such as 



80 A PRACTICAL TREATISE ON FOUNDATIONS. 

winds, as the floors, partitions, roofs, etc., prevent this ; over- 
weighted floors might exert this tendency, but in this case the 
floors would have to give way to cause any dangerous effects, 
but at the same time there would be an outward tendency 
also. Both of these effects, whatever be their relative value, 
can be provided against by some simple device for anchoring 
the joists to the walls, which would at the same time give 
proper play for expansion, and give ventilation to the ends of 
the joist. One form of this is an iron casting with a rib at the 
bottom, a notch being made in the joist to fit over it. This 
anchoring prevents the walls from overturning outward in 
warehouses where large quantities of grain and other like 
material are stored. The roof also, in some cases, has a ten- 
dency to overturn the wall, as in the Gothic roof-truss, where 
no tie-beam is used. In all such cases the thickness of the 
walls must be increased, or it must be stiffened by buttresses. 
A standing wall of brick is considered the best and surest bar- 
rier to resist the spread of flames. 

152. If walls of brick, such as house walls, give way by slid- 
ing, bulging, or overturning, the plane or line of breaking will 
follow the mortar-joints, as the resistance to the tendencies 
depends mainly upon the adhesion of the mortar to the brick, 
or the tensile strength of the mortar itself ; therefore for the 
greatest strength the mortar used should be at least as strong 
as the brick itself. This can only be realized, however, by the 
use of cement mortar, as lime mortar will never be as strong as 
good brick, and as too often used is not much better than so 
much mud ; often hardly enough lime is used to cover the grains 
of sand, and it is not unusual to see the mortar eaten out from 
5 to 10 feet above the ground, apparently caused by water 
absorbed from the ground. 

153. As to the adhesion of the mortar to the brick, it is 
hard to determine its value, as it depends to a very large extent 
upon the character of the brick and on the condition of its sur- 
face : if the brick is dry and dusty, the adhesion will be very 
small ; if the brick is porous, clean, and wet, it will be of consid- 
erable value. It is inexcusable to lay brick unless they are 



BRICK. 8t 

thoroughly wet or even saturated with water; but masons will' 1 
not take this trouble unless compelled to do so, even in hot 
weather, and as a consequence the brick separates from the 
mortar with a perfectly clean surface. In the contrary cases it 
is often difficult, if not impossible, to remove the mortar from 
the faces of the brick. Always wet and keep the brick wet. 

154. If what has been said is true, brick should never be 
used below ground unless good cement mortar is used, and it 
is always better to use stone even then. Dampness can be 
prevented from rising in the walls above the ground by using 
one or two layers of slate in the mortar-joints. Lime and! 
cement can be mixed, using one barrel of lime and one barrel/ 
of cement, or even two of lime and one of cement would be 
vastly better than all lime. 

155. There is a variety of hard strong bricks called com- 
pressed bricks : these are generally of good shape, square angles, 
true and parallel surfaces, made in different parts of the coun- 
try ; but these, owing to their great cost, are scarcely used ex- 
cept for facing walls, jams and lintels of doors and windows, 
cornices, etc. Walls faced in the ordinary way are hardly to be 
recommended, as in any case they are but poorly bonded into 
the back of the wall ; this arises from several causes : the com- 
pressed bricks are not of the same sizes as the ordinary, -and in 
addition it seems to be the practice to lay the facing with very 
thin mortar-joints, and to this add the ordinary carelessness in 
building the back walls. The monotonous red of these bricks 
and the unbroken uniformity in color does not always add to 
the appearance of such buildings. 

156. A good safe rule for the thickness of the walls of 
houses would be not less than 12 inches at top, and an increase 
of 2 inches for each 12 feet to the bottom ; this for a wall 50 
feet high would be 20 inches at the ground line. It should 
seldom be thinner than this, and for warehouses and depots 
it should be from i| to 2 times the above, according to cir- 
cumstances. 

157. Brick is also largely used in sewers, which are gener- 
ally circular or oval in cross-section. 



82 A PRACTICAL TREATISE ON FOUNDATIONS. 

158. Brick pavements for streets have been used to a large 
extent in some localities and seem to give satisfaction, are 
claimed to be durable, easily cleaned, comparatively noiseless, 
and favoring a good foothold for horses. Bricks for this pur- 
pose should be hard and sound, and of the best quality, as they 
have to stand wear from both shocks and friction, to which 
ordinary structures are not exposed. For this purpose there 
is not perhaps sufficient experience or data to make a com- 
parison with other paving materials. 



Art. XVI. 
BRICK ARCHES. 

159. BRICKS are used very largely in building arches, es- 
pecially over openings in ordinary houses, such as doors and 
windows, and at the bottom of walls to keep them from being 
pressed inwards, and at the same time they serve to distribute 
the pressure over the space between the walls ; in this case they 
are called inverted arches. 

160. Ordinarily arch rings of brick consist of one, two, or 
more rings of brick, laid as stretchers, these rings being only 
held together by the adhesion of the mortar between them to 
the brick, and by the tenacity of the mortar. As seen above, 
the line of pressure in an arch is not always a symmetrical or 
regular curve, and consequently the entire pressure, or at any 
rate a large part of it, will be concentrated on one of the rings 
of brick, which might result in crushing the brick or in separat- 
ing the rings. 

161. There are only two methods by which this difficulty 
can be overcome : 1st, hy having wedge-shaped bricks made es- 
pecially for the purpose, which can either be equal to the thick- 
ness of the arch ring, or can be laid as header and stretcher, 
thereby distributing the pressure ; 2d, the arch can be so built, 
by regulating the thickness of the joints, that at intervals the 
mdiating joints of the several rings shall be in the same plane, 



BRICK ARCHES. 83 

so that headers may be introduced, resulting in a distribution 
of the pressure. 

162. Owing to the fact that arches, properly speaking, are 
built according to the curve of circle or an ellipse or a com- 
bination of these, the outside rings will be a little longer than 
the inner rings, and as a consequence with ordinary bricks the 
joints will have to be a little thicker on the outside rings. This 
is regulated by laying the inner rings with a very little space 
between the bricks, and gradually increasing in thickness to 
the outer rings, or the increased space in the outer rings can be 
partly filled with pieces of ordinary slate, which answer well 
the purpose. 

163. The strength of brick piers or arches can be materially 
increased by the use of ordinary hoop iron, bent into the joints 
and under and over the bricks : it is easily and simply applied, 
economical, and can be recommended ; will also strengthen 
concrete and cement pipes. Wire netting is also used. 

164. In the lining of tunnels which are arches, the side 
walls or abutments are continuations of the arch to the bottom, 
the foot of the walls being joined by inverted arches. Tunnels 
are generally lined with brick, on account of the ease with 
which brick-work can be built, especially in confined and 
cramped positions. Often tunnels are lined with timber ; this, 
however, is only a temporary and economical expedient. This 
will be further alluded to under the subject of timber. 

165. The thickness of tunnel arches can only be fixed by 
empirical rules, based upon the practice that has existed through 
the past ages, as the condition of the external forces are not 
thoroughly understood ; but in case of tunnels, especially those 
at great depth, the pressure is practically uniform and constant, 
and the line of pressure is fixed and not altered by rolling 
loads, as is the case with arches built under ordinary conditions. 
The cross-section of a tunnel through ordinary earth requir- 
ing a lining is generally two-thirds to three-fourths of an ellipse ; 
in rock it may be said to be of any shape most conveniently 
excavated, giving ample room for the purpose intended. 
Thickness of arching varies from 20 to 36 inches. 



84 A PRACTICAL TREATISE ON FOUNDATIONS. 

166. Arches are used largely for crossing streams, streets, 
roads, either over or under, of varying lengths and spans. 
The abutments of arches generally have wing walls con- 
structed in one of the methods above described and for the 
same purposes. These wing walls are sometimes built on a 
curved batter ; the principles of construction are, however, 
the same. 

167. The principles of brick arches as to stability are the 
same as in stone-masonry arches. The line of pressure is con- 
structed in the same manner, the depth of the arch ring can be 
found by the formula for masonry arches, but these results 
should be increased by at least 25 per cent ; that is, if the for- 
mula calls for 2 feet of masonry, it should be at least 2.5 to 3 
feet thick for the brick arch, but this is generally stated as so 
many rings ; as the brick is placed flatwise as stretchers, each 
ring would be about 4^ inches thick ; this with the mortar-joints 
would take about 8 rings or courses. 

168. Many large arches have been built of brick, but as a 
rule it is used mainly for very small arches, stone being pre- 
ferred wherever it can be obtained conveniently and economi- 
cally. It is not an unusual plan to make the end ring-courses 
of ashlar masonry, and between the two ends build the ring 
of brick. In order to secure a good bond, three or more 
string-courses of stone masonry could be used, the brick rings 
abutting against these stones; this is not, however, commonly 
resorted to. 

169. Brick-work is estimated and paid for either by the 
cubic yard or surface measurement. In the first case it is usual 
to state that so many brick shall make a cubic yard ; this is 
generally estimated at about five hundred bricks ; it, however, 
depends upon the size of the brick and the thickness of the 
mortar-joints. In the second a square or perch on the face of 
a wall one brick thick is the basis of estimate ; if the wall is two 
bricks thick, the surface is supposed double : this on the face of 
the wall includes openings either in part or entirely, according, 
to the agreement. 



ARCHES. 85 

Art. XVII. 
CONCLUSIONS. 

170. We may therefore sum up as follows, in regard to the 
theories of the arch, and their practicable application : 

171. The stability of the arch, as of all structures, depends 
upon the relations existing between the external forces or loads 
tending to produce strain, and the internal forces or stresses 
thus developed tending to resist or balance the external forces. 
In all discussions of walls or arches the length is considered as 
unity ; that reduces the wall under consideration to the value 
of a section of the wall or arch included between two planes 
perpendicular to its axis at a unit distance apart, or simply 
equivalent to the area of the cross-section. 

172. The external forces to be considered are the forces or 
loads acting upon the structure of whatever nature they may 
be, including the weight of the structure itself, and the sup- 
porting forces, whether applied to the whole structure, in which 
the supporting pressure is the resistance of the foundation, or 
whether applied to any portion of the structure, no matter how 
small into which it maybe divided. In this case the supporting 
forces are the forces or stresses exerted between the portions 
of the structure under consideration and the other portions in 
contact with them : the conditions of equilibrium require that 
these shall balance each other. 

173. A force is completely determined when its point of 
application, its direction, and its magnitude are fully known. 

174- We are met, in deducing any theoretical formula for 
these relations, in the beginning, with a great want of knowledge 
as to either of these elements of force, and in fact the accurate 
determination is impossible. 

175* As a consequence a great many suppositions have 
been made, and upon each supposition some theory has been 
constructed ; and as the premises differ widely, so do the con- 
.clusions. 



86 A PRACTICAL TREATISE ON FOUNDATIONS. 

176. We do not know the pressure exerted by earth against 
a retaining-wall in either of its essential elements, and less do 
we know the pressure exerted upon an arch loaded with earth 
or other material, and in addition with heavy rolling loads. In 
arches, however, the assumption is made that the entire load 
above acts vertically, and with its full intensity upon the arch 
ring ; this is certainly on the side of safety, eliminating all in- 
clined or horizontal forces of any kind. The second assumption 
is that the arch ring supports this entire load : this naturally 
follows from the first. The third assumption is as to the point 
of application and direction of the thrust or stresses developed 
in the arch ring; these, however, being assumed, the magnitude 
of the thrust itself can be easily determined. 

177. Every change, under the same external loads or forces,. 
in the direction or point of application of the thrust gives an 
entirely different line of pressure, upon the position of which 
the stability of the arch is supposed to depend, and there may 
be any number of lines of pressure ; the problem of determining 
the true line is evidently indeterminate. 

178. The pressure at the crown is supposed to be horizontal, 
and must have its point of application in the arch ring itself, 
and generally in the middle third of its depth. 

179. With these quantities assumed, together with observing 
the manner in which arches give way, we are enabled to de- 
termine with some degree of approximation the requisite depth 
and thickness of the arch ring for any given form and size of 
arch. 

180. Arches give way either by crushing the voussoirs, or 
by the parts sliding on each other at some of the joints, or by 
the parts rotating either around the outer or inner edge of the 
arch ring. 

181. To prevent crushing the arch stones, the intensity of the 
pressure must not be greater than the strength of the stone, and 
for safety not more than one-tenth of their strength. It should 
be uniformly distributed over the depth of the arch ring, or at 
any rate it should not vary from uniformity further than that 
which can be represented by the ordinate of a right-angled tri- 



ARCHES. 87 

angle whose base is the depth of the arch ring, and whose 
height is double the mean pressure, found by dividing the total 
pressure on any joint by the depth of the joint (which is the 
area of a unit of length); in this case the pressure at either the 
intrados or extrados would be nothing. In other words, the 
greatest intensity of the pressure at any point must not exceed 
two times the mean pressure, supposing the total pressure to 
be uniformly distributed. 

182. When sliding takes place, unless caused by settlement 
of one of the abutments, it will generally occur at four joints 
of the arch ring, splitting it into five parts : in flat arches the 
upper parts sliding downwards and two parts on either side 
sliding outwards ; in pointed arches the upper part sliding 
upwards and the other two sliding inwards. To avoid this the 
resultant pressure at any joint should not make with the nor- 
mal to the joint an angle greater than the angle of repose. 
Radiating joints will generally fulfil this condition ; if not, the 
direction of the joints can be easily changed. 

183. When arches give way by rotating or overturning 
around any joint it will generally occur at five points, — one at 
the crown, two at some point between the crown and the 
springing and two at the springing, — dividing the arch ring into 
four parts ; in flat arches the two upper parts falling inwards or 
downwards, and the two lower parts outwards, and in pointed 
arches the reverse. This will be prevented by confining the 
line of pressure within the arch ring, and for perfect safety 
within the middle third. Wherever the arch ring opens is a 
joint of rupture, but we generally speak of the joints of rupture 
as applying to the joints on either side of the crown, between 
the springing and the crown. The exact position of the joint 
of rupture cannot be determined, but is supposed to be be- 
tween those joints that make an angle from 30 to 45 degrees 
with the horizontal. 

184. The general modes of determining the line of pressure 
graphically have been explained. 

185. While building the arch ring it must be supported by 
a frame called the centre ; this is generally made of timber. 



/ 

SS A PRACTICAL TREATISE ON FOUNDATIONS. 

For small arches it consists of an arch rib composed of two or 
more layers of plank, cut into short pieces of from 5 to 6 feet, 
so that when cut to the form of the arch they will be about 12 
inches deep at centre and 8 inches deep at ends, with radial 
ends; these are bolted together so as to break joints; iron 
straps are generally placed over the joints and bolted. The 
upper surface is cut accurately to the form of the curve ; this rib 
is connected with a tie-beam, which is generally two pieces of 
plank bolted to the rib, from which springs one or more ver- 
tical and radiating struts to support the rib. These frames 
rest on vertical supports ; which are generally capped with tim- 
ber, and between the tie-beam of the rib and the cap of the 
supports queen or double wedges are driven so as to bring the 
arch accurately to its proper position. These frames are 
placed at short intervals, depending upon the size of the arch 
and the strength of the frames. Over these frames and per- 
pendicular to them are placed scantlings or laggings, so as to 
form a close sheeting to support the arch stones. In very 
large arches the centres are composed of strong timber bow- 
string girders, supported and braced by as many direct sup- 
ports as practicable. It is necessary that the ribs of these 
frames should be practically rigid or unyielding, as a small 
yield or spring anywhere might result injuriously. The stones 
do not commence to bear on the centre until the joint is reached 
at which the stones would begin to slide on each other, and in- 
creasing then in a rapid ratio to the crown, and only becomes 
self-supporting when the key-stones are put in position. 

186. A good part of the arch, from the springing on each 
side, can be built without the aid of centres, and by a liberal 
use of hoop iron, especially in brick arches, no centres need be 
used at all. Centres are not removed until the mortar has 
had time to dry. 



\ 

BOX CULVERTS. 8g 

Article XVIII. 
BOX CULVERTS. 

187. THERE is another structure, very small, and seemingly 
•so unimportant that it is scarcely ever noticed, but at the same 
time used largely: this is the box culvert, which can be built 
of stone, brick, or timber, and is used to carry small streams 
under embankments. It consists essentially of two walls, 1, 2, 
or 3 feet apart, generally i£to 2 feet thick and covered over 
the top with large flat stones ; the height of the walls vary be- 
tween 2 and 5 feet high ; if larger than the above size should 
be required to carry off the water, it is usually built double, 
that is, two side walls and a middle wall, mainly on account of 
the difficulty in securing such large capping-stones as would be 
required. The ends can be left rough or neatly finished, and 
have small wing walls : its length in this case will be a little 
shorter than the total width of the embankment at the bottom ; 
if no wing-walls and no spandrels are used, the total length 
must be equal to or greater than that width. At the ends an 
apron wall is built ; a trench is dug two or more feet deeper 
than the foundation of the side walls, and perpendicular to the 
axis of the culvert, and built up with masonry, the object of 
which is to prevent the undermining action of the stream, the 
bottom of the culvert is generally paved with small stones; the 
embankment is then built over the culvert. Arches for the 
same purpose commonly have the apron walls, and are paved 
in the same manner. Arches are used when an opening more 
than 5 feet wide is required to pass the water. 

188. In filling over arches and culverts, special care must 
be taken not to endanger the stability by shocks ; the earth 
should be deposited on both sides at the same time, thrown 
by shovels, and should be rammed in place ; this should be 
done for about IO feet on both sides and on top, after which 
the earth can be dumped on in the usual manner. This pre- 
caution is quite an important one, and should not be neg- 
lected. 



90 A PRACTICAL TREATISE ON FOUNDATIONS. 

189. For the purpose of carrying small streams under 
embankments, terra-cotta pipes, owing to their comparative 
cheapness, are now largely used in sizes from 6 inches to 2 feet 
A special bed of sand or fine earth should first be prepared to 
receive the pipes, otherwise they are likely to be broken or 
distorted bv the weight ; the earth over and around them 
should be carefully placed and packed ; the ends should gen- 
erally rest in masonry head walls of some kind ; the joints 
should be filled with cement. 

GENERAL FRIXCIFLES. 

Certain general rules or principles should be followed in 
constructing masonry structures. 

190. The courses of masonry should, in general, be laid 
perpendicular to the resultant pressure: in ordinary cases hori- 
zontal courses will satisfy this condition well enough. 

191. The vertical joints should not be continuous, but 
should be broken from course to course by overlapping the 
stones by a distance equal to the depth of the course, which 
in ashlar should not be less than one foot. This is known as 
the bond. A sufficient number of headers should be used to 
tie the wall together transversely, and these should be placed 
as nearly over the centre of the stretchers below as possible. 

192. All joints and spaces between the stones should be 
fully filled with mortar. 

193. Stratified stones should be laid on their natural beds. 
— generally known as the quarry bed. 

194. The surfaces of porous stones should be moistened be- 
fore being placed in position; this is essential with sandstone 
and brick. For appearance' sake, the largest stones should 
be placed near the bottom, the thickness of the courses gradu- 
ally decreasing towards the top. A good rule for the lengths 
of the headers is to make them equal to ^ the thickness of the 
wall at the point where placed, provided that they will not ex- 
ceed 6 feet in length. All the above except the last applies 
equally to brick-work. 

195. Good brick should be regular in shape, opposite plane 



CEMENT. 91 

surfaces parallel to each other, and all angles right angles ; 
should give a clear ringing sound when struck ; should show on 
a broken surface a hard, compact and uniform structure; and 
should not absorb more than one fifteenth of their weight of 
water. 

Article XIX. 

CEMENT. 

196. THE term Hydraulic Cement, or simply Cement, is 
applied to those substances, whether natural or artificial, which, 
when calcined and ground into powder and mixed with water, 
form a paste possessing the property of hardening under water. 
There is almost an infinite variety of these stones, found in 
layers or strata of different thicknesses, in the States of New 
York, Pennsylvania, Maryland, Virginia, Tennessee, and other 
States. These different strata, whether found in the same 
locality overlying each other, or in the same neighborhood, or 
in the different States, are found to be of different composi- 
tion, and when treated in the same way yield products dif- 
fering in a marked degree in regard to their hydraulic activity 
or rapidity of setting, and in hydraulic energy, or that property 
by which, whether they set rapidly or slowly, they attain a 
great and progressively increasing strength. Some take an 
initial set rapidly, but seem to increase in strength and hard- 
ness very slowly afterwards ; others are slower in taking the 
initial set, but show a more regular and continuous increase in 
hardness than the first, and ultimately are far better. This 
difference is due not only to variations in composition, but 
also in a large degree to the degree of heat and the time con- 
sumed in the burning so much so, that some of them only 
partly calcined possess little or no hydraulic energy; others, if 
at all overburnt, lose this property. In order, therefore, to 
produce a cement that will neither have too great nor too 
little hydraulic activity, and therefore better suited for ordinary 
purposes, the manufacturers mix the different grades of crude 
material, and obtain a product which is a more or less homo- 



92 A PRACTICAL TREATISE ON FOUNDATIONS. 

geneous mixture of the several grades. This may explain the 
want of uniformity so often found in the same brand of cement 
obtained at different times. Frequently, in works of great 
magnitude continuing through a period of years, requiring 
large quantities of cement, some cargoes show a marked differ- 
ence in the time of setting : even with every precaution an 
ordinary batch of mortar will show signs of stiffening and set- 
ting before it can be used, resulting often, under strict inspec- 
tion, in much waste, and again so slow in setting as to arouse 
suspicion that the entire cargo of cement is of an inferior grade. 
The writer has often seen some cements so quick in setting 
that they would stiffen to such a degree in the short interval 
required to lift the boxes and land them on the top of the pier, 
that it would be necessary to work the mortar again before 
using, the interval being not over 5 to 10 minutes, and in other 
cases after standing all night little or no appreciable change 
had taken place. The above cements are generally called the 
light quick-setting cements, weigh about 300 lbs. per barrel, 
and set in 5 minutes to 4 or 5 hours; are calcined. at a moderate 
temperature, when 7 days old, 6 days in water, should have a 
tensile strength of not less than 60 lbs. per square inch and 
contain from 20 to 40 per cent of clay. These cements are 
generally known as the Rosendales, the Cumberland, Round 
Top, James River, Louisville, etc. ; are found, respectively, in 
New York, Maryland, Virginia, and Kentucky. 

197. What are known as the heavy, slow-setting cements 
are almost entirely artificial products, and are commonly known 
as Portland cements, such as the German, English, French, and 
American brands. They are composed of pure clay and lime 
containing from 20 to 25 per cent of clay, are calcined at a very 
high temperature, weigh about 400 lbs. per barrel, and should 
have a tensile strength of 1S0 lbs. when 7 days old, 6 days in 
water. These cements possess both great hydraulic activity 
and energy, and are far superior in every respect to the natural 
cements. 

198. The temperature of the air and water have much to 
do with the setting of cements, and affect them in different 



CEMENT. 93. 

degrees. As illustrating this, the writer noticed that Alsen's 
German Portland cement mortar was being delivered to the 
crib smoking and hot, and on being emptied from the box the 
rr.ass fell to pieces as damp sand would do, and showing evi- 
dently an initial set. Upon inquiring into the cause, he found 
that for some reason hot water was being delivered through 
the pump ; this happened on several occasions, — the time 
of passing from the mixer to the crib could not have been 
over 3 to 5 minutes, — and caused some considerable waste. 
This was ascribed by the men at first to what they called hot 
barrels, but was found to be due to the use of hot water. 
Concrete in the working chambers of caissons will set almost 
immediately, the temperature ranging from 8o° to 90 Fahr., 
or more, and after standing 24 hours will require blasting to 
remove it. This was done in a caisson at the Schuylkill River. 
The result is the same whether mixed with hot water, immersed 
in hot water, or placed in a hot atmosphere. Some engineers 
require the cement and broken stone to be carried separately 
into the caisson and mixed below on this account. It may 
have some advantages, but the disadvantages would seem to 
be greater. The ingredients are not likely to be mixed as care- 
fully or as thoroughly, they would be exposed for a longer 
time to the hot air of the working chamber, which is frequently 
very dry, and in addition will be more expensive. The writer 
always required one or two bucketsful of water to be poured 
into the supply shaft just before throwing in the concrete. This 
concrete was never mixed until a signal was given from below 
that they were ready for the concrete ; the sand and cement 
were ready mixed, broken stone collected ; it would then take 
only a few minutes to make the concrete, which was thrown im- 
mediately into the shaft. The compressed air passes rapidly into 
the shaft, the concrete drops on a platform and is immediately 
wheeled by barrows or shovelled into its place, deposited and 
rammed, the entire time consumed being not over 10 to 15 
minutes. In this connection Gen. Gillmore mentions, page 81, 
that of two samples of cement paste, which set in 90 Fahr. in 
l| and 4 minutes, required at 65 , 6 and 17 min., and at 35 , 39 



94 A PRACTICAL TREATISE ON FOUNDATIONS. 

and 82 min., respectively, to get the same set ; i.e., for a depres- 
sion of temperature from 90 to 35 = 55 , the delay in setting 
to the same extent was 37^ minutes in one case and 1 hour 
and 18 minutes in the other, and concludes that the presence 
of an excess of caustic lime in some of the varieties of cement 
causes them to be quick-setting, due to the heat developed in 
bringing this lime to a state of hydrate. 

199. What is meant by a "set " is not well defined. Gen. 
Gillmore defines it as a state of the paste in which it will not 
change its form without fracture, or when it has entirely lost 
its plasticity ;" this is evidently a vague and uncertain standard 
of comparison. Another test of the setting is the time that is 
requisite for the mortar to bear a small wire loaded with a cer- 
tain weight, — a J^-inch wire loaded with \ pound, and a ^-inch 
wire loaded with 1 pound ; and when the mortar will support 
these weights without indentation or depression it is said to 
have " set." The latter is purely a surface test, and as the tem- 
perature of the air and water play such an important part in 
determining the time of taking a set, its value is only for 
comparison of the hydraulic activity of two or more different 
brands, and would vary greatly according to the time of the 
year, and can be of but little practical value, as the cement 
may be tested at one time and used at another. If the tensile 
strength is taken as the standard, the Portland cements should 
be called the quick-setting, and the ordinary cements-slow-set- 
ting. In practice, however, the distinction is not of very great 
importance, as most cements, when mixed in small quantities, 
afford ample time for using before any harmful change takes 
place in the mortar ; but this is not, however, universal. A 
quick-setting cement has some advantages when exposed to 
immediate causes of deterioration or destruction, as when used 
in sea-water, works under such circumstances being constructed 
at low tide, and shortly flooded by high tide ; under such cir- 
cumstances a slow-setting cement could be used and faced, or 
protected by an inferior but very quick-setting cement. 

200. is Quick-lime ordinarily slaked by pouring the entire 
quantity of water necessary on the lime at one time, — about 



CEMENT. 95 

two or three times the volume of the quick-lime. After slak- 
ing has commenced an addition of cold water is injurious. Good 
lime should not require stirring or the breaking of lumps dur- 
ing slaking. The same method is adopted in adding water to 
cement, but as this is mixed immediately before using, it is 
important not to use too much water, as the mortar will be too 
soft, and to avoid this the general practice is to mix the mor- 
tar at first rather dry, and then temper it with a small addition 
■of water, to the proper consistency. This is preferable to mak- 
ing it too soft and wet at first, and then adding dry cement 
powder to bring it to a proper plastic condition. 

The quantity of water necessary in mixing cement varies 
materially with the kind of cement used, the condition of the 
weather as to heat, moisture, or dryness, the age of the cement, 
whether dry or moist sand is used, and whether the broken 
stone is moist or dry. To form a paste of cement mortar of 
ordinary consistency I bbl. of cement will require about \ of a 
barrel of water, but when sand is used more water will be re- 
quired ; but this excess should be added in small quantities, as 
at a certain plastic state even small quantities of water will 
make the mortar too soft. An ordinary cement barrel con- 
tains 3f cubic feet of space, and about 5 cubic feet of loose 
cement can be packed in the barrels. Mixed in the above 
proportions there will result about § of a barrel of paste. In 
some cases the sand is mixed with the paste, but the general 
practice is to first mix the sand and cement dry. These should 
be turned over and over until it has a uniform appearance. 
When carelessly mixed, patches or layers of cement without 
■sand and sand without cement are readily seen, and if water 
is added in this condition it will be impossible to secure a 
homogeneous mortar. I barrel of cement, 2 barrels of sand, 
will make from 8 to Z\ cubic feet of mortar, which will ordi- 
narily be sufficient for laying 1 cubic yard of brick-work or 
hammer-dressed rubble-work, and in making 1 cubic yard of 
concrete. And 1 barrel of cement, 3 barrels of sand, will 
make about 12 cubic feet of mortar, sufficient for i|- cubic 
yards of ordinary masonry and concrete. Rough rubble will 



96 A PRACTICAL TREATISE ON FOUNDATIONS. 

require from 11 to 12 cubic feet of mortar per cubic yard, or \\ 
barrels of cement per cubic yard ; if mixed, 1 cement, 2 sand, 
or 1 barrel of cement ; if mixed, 1 cement, 3 sand. 1 barrel of 
cement should be sufficient for \\ cubic yards of good ashlar 
masonry. For quick-lime mortar only about h, of the above 
is necessary, \ barrel of lime being equivalent to 1 barrel of 
cement. The above quantities are fair approximations, and 
will serve as a good basis for estimating the number of barrels 
of cement used in any proposed construction of masonry, 
whether ashlar, brick, concrete, or rubble, and consequently 
the cost of the same per cubic yard. 

201. Mr. Trautwine, in edition of 1888, gives the following: 





Tensile strength, 

7 days old, 
6 days in water, 
in lbs. per sq. in. 


Crushing strength, 

7 days old, 

6 days in water, 

in lbs. per sq. in. 


Tons per 
sq. ft. 


Portland Cement (neat), . . 

" " (2 sand), 
American " (neat), . . . 

" " (2 sand), . 


170 to 370 
22 "126 
40 " 70 
22 


1100 to 2500 

I IOO " 2500 

250 " 450 


71 to 154 

71 " 154 

16 " 291 



The practical engineer will rarely be able to do more than 
determine the tensile strength, as described in another para- 
graph. The above results seem to be low, and any cement not 
showing a strength equal to the inferior limits of 170 and 40 
lbs. as above should be rejected. For Portland cement it is 
not unusual to specify that at the age of 7 days, 6 days in water 
the tensile strength should be at least 300 lbs. per square inch, 
and sometimes as high as 500 lbs., and for the American brands, 
such as the Rosendale, Louisville, etc., should certainly never 
fall below 40 lbs., and should be required to stand the superior 
limit of 70 lbs. in the time specified. 

Article XX. 

MORTAR. 

202. MORTAR is a mixture of lime or cement, sand, and 
water in certain more or less definite proportions. It is usual 
to prescribe the proportions of lime or cement to that of sand 



MORTAR. 97 

as I to I, i to 2, i to 3, etc, the proportion of sand depending 
upon the kind of cement and nature and importance of the 
work. Sometimes these proportions mean by volume, some- 
times by weight, the amount of water being regulated somewhat 
arbitrarily. For ordinary walls quick-lime is generally used ; 
for more important works cement : sometimes the two are 
mixed. The volume of mortar varies from one eighth to one 
third the volume of stone, the larger limit in concrete and rub- 
ble. It is stated on good authority that one volume of lime 
paste can be mixed with one volume of cement paste without 
material loss of strength, and that a mixture of lime paste equal 
to one half or three fourths that of the cement paste produces 
no appreciable injury, and is suitable for concrete when under 
water, and even better on many accounts. When not imme- 
diately immersed, it has the advantage of making some quick- 
setting cement slower in setting, and is certainly economical. 
The practice, however, differs, and it can be safely said that 
there is a very decided prejudice against this mixture. 

203. Quick-lime is the product resulting from burning lime- 
stone in a proper constructed kiln, the heat driving off the car- 
bonic acid, leaving white lumps and powder, which is the lime 
of commerce ; this when mixed with water undergoes " slak- 
ing," a chemical action being set up, the water combining with 
the lime, which in the process falls to powder and results in a 
stiff white paste. The volume swells and great heat is developed. 
The perfectness of this process is probably the best and surest 
test of the quality ; the presence of lumps or cores that will not 
slake means either an inferior quality of lime or insufficient 
burning, and results in great waste. 

204. The proportions of sand and lime vary from 3 to 6 vol- 
umes of sand to one volume of quick-lime ; the mortar thus 
procured is used extensively in walls of houses, and even in 
more important structures, but should never be used under 
ground or under water, as it will not attain any great degree of 
hardness under these conditions, if it hardens at all ; that this 
is often done, only proves that our structures are many times 
stronger than required. Lime mortar should never be used in 



98 A PRACTICAL TREATISE OAT FOUNDATIONS. 

concrete in large masses, as it may be doubted if the interior 
of the mass will ever harden, as lime mortar sets alone by ab- 
sorbing carbonic acid from the air, returning to the condition 
of a carbonate of lime, the cemented material then becoming 
an artificial sandstone. Cement mortars set by chemical 
action, and probably throughout the entire mass at the same 
time. 

205. The ordinary limestone contains other ingredients such 
as silica, alumina, magnesia, in such small proportions, say not 
to exceed 10 per cent, that they exert no beneficial or harm- 
ful influence worth considering, but when we find limestone 
which contains these elements in proportions between 10 to 60 
per cent, we find stones that possess peculiar properties, and of 
immense value and importance. The writer, in what he has 
said on this subject and what follows, does not propose to enter 
into the refinements of this subject, but to present a few facts 
which occur to him, of the greatest practical value. Those who 
desire can find a great deal of most interesting and valuable 
information, and doubtless the best available (up to time of 
publication, 1872) in Gillmore's book on limes, hydraulic cem- 
ents, and mortars. 

206. Cement stones exist in all states, from the very slightly 
hydraulic to the intensely so, culminating in the Portland cem- 
ents, which are artificial products resulting from the mixture 
of pure clay and pure limestone in certain definite proportions 
determined by experiment, thoroughly mixed and calcined at 
a very high temperature, then ground to a fine powder. Port- 
land cement is of course the best in every respect, but it is 
very expensive, and consequently only used in certain special 
structures of great magnitude and importance. For ordinary 
purposes requiring the use of hydraulic cement, the natural 
stone possessing hydraulic properties is calcined in a kiln, 
thoroughly ground and barrelled for use. These natural stones 
are found in many parts of the Middle States, each varying in 
some respect ; some very-slow setting, some very quick-setting, 
and other medium ; generally when ground of a mouse color, 
but some decidedly yellow. It cannot be denied that some very 



MORTAR. 99 

inferior grades are put upon the market, and without careful 
testing, are used, but as a rule the standard companies cannot 
afford to take the risk of such conduct, and can be relied on in 
the main. 

207. As to different cement brands, we must first be guided 
by tests that have been made, and select that one which seems 
best suited for the purpose in view, and in addition simple test, 
should be made on delivery. All broken barrels should be re- 
jected, especially if it is to be stored for any length of time, as 
by exposure to the air it will take a set and be useless, and as 
it also results in waste. On opening barrels small portions 
found to be set will not necessarily indicate- that the balance 
is ruined ; but it excites suspicion of undue age or exposure, and 
means so much waste. 

208. It is well to test a fair number of barrels by inserting 
the hand into the mass of cement, principally to determine the 
fineness to which it is ground, as a little experience will enable 
you to measure the sensitiveness of the touch ; but this can 
easily be verified by obtaining a sieve with small meshes, num- 
bered according to the number of meshes to the square inch. 
A No. 60 sieve would contain 3600 meshes to the square inch, 
a number 50 sieve 2500 to the square inch ; this last ought to 
pass the entire quantity, except a small per cent ; the coarser 
particles add nothing to the value of the cement, and amount 
to so much waste. In addition, small cakes of mortar made 
with good sand and cement in proportion used on the work 
will give a very good idea of its setting qualities either in air 
or water. 

209. Where large quantities of cement are being delivered 
and used more or less rapidly, the above are the only tests 
practicable, and using the standard brands, it will determine 
practically whether the cargo under consideration is up to the 
standard. A medium, slow-setting cement is preferable, other 
things being equal, to a very quick-setting cement, as in large 
works the mortar will have to stand for some little time before 
being used entirely ; this should be avoided as far as possible. 

210. In general, you can rely on the Portland cements, 



L.of C 



lOO A PRACTICAL TREATISE ON FOUNDATIONS. 

German, English, or American brands, for any purpose ; the 
Rosendale, Norton, and Hoffman brands, the Louisville, James 
River, Va., and many other brands have generally given entire 
satisfaction in the writer's experience. The writer has had 
but little experience with lime and cement mixed, but experi- 
ment as well as experience seem to authorize the use of it in 
the proportions above mentioned, and it certainly possesses 
the advantage of economy. 

211. There have been comparatively few experiments made 
to determine the resistance to crushing of mortars when 
mixed with sand, and it has been the practice to determine 
the tensile strength of the many brands of cement, and from 
these results the crushing strength is, to a great extent, in- 
ferred, on the supposition that a high tensile strength indicates 
a high crushing strength. Many and varied experiments have 
been made in this manner. 

212. Briquettes of neat cement, and mixed with varying 
proportions of sand, i to I, i to 2, I to 3, have been tested. 
These briquettes have rounded ends, connected by a square 
prism of exactly I square inch cross-section ; they are so 
formed that they will break at some point between the heads, 
and not at the junction of the head and neck. Brass moulds of 
the proper size and shape are made, and the mortar pressed 
into the mould and allowed to get an initial set. The mould is 
then removed, and the test is made on several briquettes 
made from the same batch of mortar, at intervals of 1,2, 3, 7, 
10 and more days. The testing machines are provided with 
nippers or clutches, and so adjusted as to take hold of the head 
exactly at the junction of the head and neck, and so situated 
as to make the pull exactly in a straight line, with no twisting 
or jerking, the power being slowly and gradually increased 
until the briquette is pulled apart; and it is generally specified 
on important works that the tensile strength should be so 
many pounds per square inch, in so many days after mixing. 
Machines and moulds are specially made for this purpose, and 
it would be useless to enter into any detailed description, as 
they can be more easily purchased than made to order; and 



MORTAR. IOI 

in any event, unless the work is of very great importance, and 
cement is used in large quantities, the simple tests above 
alluded to will be satisfactory. 

213. Pure, rich, or fat lime mortar hardens slowly in air by 
the absorption of carbonic acid gas, when used in compara- 
tively thin walls, but it may never harden at all in the interior 
•of large masses. It will not set or harden under water or in 
wet soils, and should therefore never be used under water 
under any circumstances, and it is false economy to use it 
under ground in damp earths. When water is added to lime 
it undergoes the processs of slaking ; great heat is evolved ; it 
swells to 2 or 3 times its original bulk, falls to a powder, and 
the resulting product is a hydrate of lime, unctuous or soapy 
to the touch, and forms a stiff paste. Lime should not be 
exposed to the air, as it will in time become air slaked, and 
materially injured. But when mixed in paste with sand, it is 
considered better to let it stand before using, and for this 
reason lime mortar is mixed in large quantities, left in piles 
and used as needed after stirring and tempering. Lime mortar 
shrinks considerably in setting. 

214. Hydraulic limes containing from 10 to 20 per cent of 
silicates harden in air or water, but somewhat slowly under 
water; they slake to some extent, but slowly, and are sup- 
posed to harden by chemical action, probably through the 
whole mass at the same time, and shrink but little in setting. 
It should not be allowed to stand any great length of time 
after being mixed with water, as it will take an initial set, 
which, when disturbed by remixing, is supposed to materially 
diminish its ultimate strength. 

215. Hydraulic cements, or simply cements, contain from 
20 to 60 per cent of silicates. The proportion of silicates to 
the proportion of carbonate of lime determine the value of the 
cement. These vary considerably, and we have accordingly 
the heavy, slow-setting cements on the one hand. These are 
called Portland cements, and generally are manufactured, using 
pure clay and pure lime mixed in definite proportions deter- 
mined by experiment. This mixture is then burned at a high 



102 A PRACTICAL TREATISE ON FOUNDATIONS. 

temperature, ground exceedingly fine, carefully packed in good,, 
strong, and tight barrels, generally lined with brown paper, in- 
order to prevent any possible absorption of moisture ; cost 
from 2 to 2^ times per barrel more than the ordinary cements ;. 
weigh considerably more per barrel, and, owing to their ten- 
dency to set quickly, should be mixed with water only a few 
minutes before using, and only in small quantities at a time. 
The more common brands are the German, English, and Amer- 
ican, all of which brands are of excellent quality, and suitable 
for any purpose, and will stand two, three, or more volumes of 
sand, and seem not to be injured. These harden rapidly in air 
or water, and attain great ultimate strength. 

216. The ordinary cements are obtained from natural 
stones, found in many parts of the country, and are known as 
the light, quick-setting cements; only weigh about two thirds 
as much, and take a very much greater time to set, and do not 
attain more than about half as much ultimate strength as the 
Portland cements, but are strong enough for almost any pur- 
pose, and, owing to their great abundance and relatively low 
cost, are used for all ordinary purposes, and can be more con- 
veniently handled, as they take more time to set, but should not 
be mixed with water any great time before being used. The 
proportion of sand is rarely over 2 to I of cement. Some 
brands of these cements set much more rapidly than others, — 
so much so that some of them could be properly called slow- 
setting. All of these cements set well in air and in water. 

217. If mortar, whether used alone or in concrete, is to be 
deposited under water, it sfTould be allowed to take an initial 
set, as otherwise the cement will almost invariably be sepa- 
rated from the sand and the stone, no matter how carefully it 
may be deposited. Perhaps the best mode of depositing con- 
crete under water is to fill open sacks or gunny sacks about 
two-thirds to three-fourths full of the concrete or mortar and 
deposit these in place, arranging them in courses, where 
practicable, header and stretcher system, and ramming each 
course as laid ; the bagging is close enough not to allow the 
cement to be washed out, but at the same time open enough 



MORTAR. IO3 

to allow the whole mass to be united and to become as com- 
pact as concrete itself. The writer used this method in the 
foundation of a pier over 100 feet high, and has also adopted 
this plan in other works of less magnitude, but never has the 
result been satisfactory when deposited under water in any- 
other manner. 

218. In whatever way mortar has been deposited under 
water, the result is at least uncertain ; and there is positive evi- 
dence that in some cases where divers have examined concrete 
thus deposited it has been found to be far from homogeneous: 
deficiency of sand and excess of cement in some places and the 
reverse in others, and the same as to the stone and cement. 
Some experiments on a large scale were made by General 
Newton, using a very large box or caisson filled with water 
and depositing the concrete therein, with every precaution 
taken in order to secure favorable results; then subsequently 
pumping the water out, and removing the sides in order to 
make a thorough examination as to its condition. The mass 
was found to be far from uniform — an excess of stone in some 
parts, excess of mortar in others ; and again excess of sand in 
places, and excess of cement in others. This could be doubt- 
less avoided to some extent by allowing the concrete to attain 
some degree of set before being deposited in the water. 
That concrete has been deposited under water in many cases 
is undoubted, and structure erected on it whTch stand ; but 
this does not fully justify the practice, and it should only be 
resorted to in cases of necessity, and generally the necessity 
can be removed by a little expenditure of money. 

219. There is another manufactured or artificial mortar 
known as Pozzuolana, a substance of volcanic origin found in 
several countries, particularly in Italy, also other substances 
called trass or terras, having nearly the same composition, and 
composed mainly of silica and alumina, likewise of volcanic 
origin. When these substances are ground fine and mixed 
with the paste of rich lime they form a substance possessing 
great hydraulic properties, and equal in strength to the emi- 
nently hydraulic limes ; sand is sometimes added. The proper 



104 A PRACTICAL TREATISE ON FOUNDATIONS. 

proportions of these several ingredients would have to be de- 
termined by experiment. These mortars were largely used in 
marine construction by the Romans. 

220. Artificial Pozzuolana is made by burning clay. Brick 
or tile dust when mixed with fat lime form a product possess- 
ing considerable hydraulic energy. " Forge scales, slags from 
iron foundries, ashes from lime-kilns, containing cinders, coal, 
and lime, are artificial pozzuolanas" (Gillmore). Some mix- 
tures of these kinds seem to be good substitutes, when for any 
reason cement is difficult to secure. 

221. These compounds as now made do not seem to stand 
the effects of sea-water, but some conflict and difference of 
opinion exist on this point. But our quick-setting cements 
made from the natural cement stones and the Portland cements 
can generally be relied upon to resist the solvent action of the 
sea-water, but they should be allowed to get a set before im- 
mersion. 

222. It is a usual practice in cold climates to suspend ma- 
sonry work of all kinds during the winter, as it is a prevalent 
opinion that the freezing of mortar unfits it for any ordinary 
purpose; in addition, work can never be done as economically 
in cold weather as at other times. As to the effects of freezing, 
opinions differ, it being maintained by some that although it 
may retard the setting, it has no ultimate injurious effects; 
others the contrary. Lime mortar, however, by best authority, 
is damaged when it alternately freezes and thaws, but not 
damaged when it remains frozen until it has set, and the same 
may be said of ordinary cement mortars. Portland cements 
are not affected even by alternately freezing and thawing. 

223. The writer has been compelled on several works of 
importance to construct masonry nearly all the winter, and in 
several cases only stopped work when the masons refused to 
stand the exposure any longer, and in such cases he anticipated 
the probability of having to remove a part of the work in the 
spring. The stones had to be warmed and thawed out before 
using; and he has also used mortar mixed with hot water. And 
after the lapse of many weeks, through freezing and thawing 



MORTAR. 105 

-weather, has found on examination that little or no damage 
was done apparently to the mortar on the top and exposed 
joints of piers thus abandoned ; the mortar was powdered to 
the depth of a few inches, which being removed, the under- 
lying mortar was as hard as could be desired in the time, and 
on no occasion does he recall that it was found necessary to 
remove any part of the structure. Mr. Trautwine makes sub- 
stantially the same statement in his book. It is, however, un- 
doubtedly best to suspend work in very cold weather. 

224. The writer made a limited number of experiments, 
when building the bridge at Gray's Ferry, Philadelphia, in this 
direction using several brands of cement. Briquettes were 
made in the form commonly used in the test for tensile 
strength, of 1 cement, 2 sand, the proportion used on the 
work. One was kept in the house and occasionally moistened ; 
this did not freeze at all. Another was frozen, then thawed out, 
and frozen again ; this was repeated several times; and another 
was allowed to remain frozen for several days. These speci- 
mens were then tested to destruction in a suitable machine. 
The result was as follows : The one not frozen at all showed 
the greatest strength, the one that remained frozen came next, 
and the one alternately frozen and thawed gave the least 
strength. A sufficient number of experiments was not made 
to deduce any general law, or to eliminate those imperfections 
in the samples that might have existed, or to remove any 
irregularity that might have occurred in producing rupture 
when in the testing-machine, such as twisting or too rapid ap- 
plication of the weights, and only gives this for what it is 
worth. 

225. Sometimes salt is mixed with the mortar to prevent 
freezing, but it is a question whether it will set at all. It produces 
a deliquescing, sloppy mass, inconvenient to handle, and re- 
maining in this state for a long time ; it is apt to disfigure the 
face of the masonry, but is frequently used. This method 
was used at the Susquehanna River bridge to a considerable 
extent. The masonry was only stopped on this work when the 
ice commenced to move, and boats could not be held in the 



106 A PRACTICAL TREATISE ON FOUNDATIONS. 

river or stone delivered to the piers, and no evidence has ex- 
isted of any damage to the mortar. 

226. Pointing-mortar for Masonry. — Pointing masonry has 
for its object the protection of the mortar in the joints ; to 
effect this the mortar should be cleaned out of the joints while 
soft to the depth of about if inches, and this should be filled 
with a specially prepared mortar, and rammed as in calking ; 
but in practice it simply means shaping the joints so as to pre- 
sent a neat appearance, and is often done to disguise an irreg- 
ular-looking joint. The pointing-mortar should be neat 
cement, or at any rate not more than 1 sand to 1 cement, and 
before being applied should be allowed to take a set, and 
tempered with a little water when ready for use. Good point- 
ing-mortar of 1 sand and 1 Louisville cement was used at Point 
Pleasant, the mortar being mixed the night before and allowed 
to remain over night, and tempered with a little water when 
used. 

Article XXI. 

SAND. 

227. Sand is essential in lime mortar, as lime paste shrinks 
and cracks on drying, but is not in cement mortar, as cement 
paste does not shrink or crack on setting, but it is used for the 
sake of economy ; it also increases resistance to crushing, but it 
diminishes the tenacity of the mortar, the proportions varying 
from 1 volume of cement to 3 of sand, to I of cement to 1 of 
sand, and in some cases more sand is used, but can hardly be 
said to be a good practice ; the common practice is I of 
cement to 2 of sand by volume. Much has been said and 
written about sand, but ordinarily we have to do the best we 
can. Pit sand is generally angular, but apt to be dirty; river 
sand, the grains are apt to be rounded, and may or may not 
be dirty. As to the size of the grains, opinions are conflicting, 
for the best sand we may say that it should be clean ; this is 
generally determined by rubbing it in the hand when damp : if 
it stains the hand it is loamy, and should be avoided. The 



STABILITY OF PIERS. XOJ 

grains should be sharp ; this is determined by rolling the sand [/ 
in the hand ; a well-defined grating sound indicates sharpness 
of grain. 

228. Sand is used with grains varying from the size of a 
pea to a very fine grain, and purely as a practical question it 
would seem to be immaterial what size is used, provided the 
grains are not so large as to cause the stones to ride upon, 
them, and to avoid this danger the sand is generally required 
to be screened. The size of the meshes of the screen depend 
upon the purpose for which the sand is used, but are commonly 
not over one eighth of an inch square ; this will not pass a 
grain much over one sixteenth of an inch square, as the 
screening is ordinarily done in practice, which would not be ob- 
jected to for any kind of work ; this would, however, be called 
a coarse sand. Other sands vary even to almost imperceptible 
powder ; but if it is really clean sand the grating sound can. 
still be detected, and the distinct grains easily seen by an 
ordinary magnifying-glass ; but this very fine sand is also ob- 
jected to, and a medium grain seems to give more satisfaction. 
Damp sand if clean when pressed in the hand will not hold its 
shape on opening the hand, but will split and fall away; this is 1 / 
probably the best test as to the cleanness of sand, as the pres- 
ence of clay or loam would cement the grains together. It is 
claimed that the finer the sand the more cement is required to 
make the mortar. Sand from salt water is objected to by 
many, unless it is well washed before using. Sand is generally 
composed of different-sized grains, which is a favorable condi- 
tion for economy. 

Article XXII. 

STABILITY OF PIERS. 

229. PIERS can give way by sliding along some horizontal 
bed-joint, or by overturning around some edge of the masonry, 
or by crushing the material of which it is made. 

230. The pressures tending to cause sliding are the force of 
the wind, the force of the current acting directly on the end of 



108 A PRACTICAL TREATISE ON FOUNDATIONS. 

the pier and crib, or acting on a mass of ice or driftwood, 
which sometimes accumulates above the pier for a greater or 
less distance on either side, and often extending from pier to 
pier. In such cases the ice or drift sinks and collects in very 
large masses, presenting a large exposed surface to the current ; 
the effect of this is to cause the current to be much more 
rapid underneath the compact mass, endangering the destruc- 
tion of the pier by undermining or scouring, and at the same 
time largely increasing the pressure on the piers. 

231. The writer has observed closely and anxiously the 
action of a large mass of drift and ice under varying condi- 
tions, and a brief description of these cases, differing entirely, 
may not be uninteresting, and in some degree instructive, 
though he is unable to add anything in the way of a formula 
or law at all practical or useful. The action may be due to 
the ice and drift while stationary, or moving as a whole or in 
detached masses. 

232. First, while Stationary. — Expansion and Contraction of 
Ice. — Ice on the surface of a lake may exert an enormous 
force, sufficient to move heavy masonry piers, caused by alter- 
nate expansion and contraction under changing temperature ; 
even if the pier is protected by a sloping surface at the water's 
edge ; the adhesion of the ice to the stone may be so great that 
it will exert against the pier a thrust due to its full crushing 
strength before it will fracture. The crushing strength of ice as 
given by different authorities varies very greatly, depending on 
its thickness, purity of water from which it is formed, and also 
with its temperature, the limits being from 400 to 1000 lbs. 
per square inch. This enormous pressure, acting over a con- 
siderable surface and often with a long lever arm, may exert a 
very great overturning moment. It is stated in Engineering 
News, Jan. 12, 1893, that a pier weighing 1000 tons was not 
only lifted, but held up under passing trains ; and piers built 
on pile foundations were thrown out of line from 2 to 12 
inches, the ice being from 10 to 12 inches thick. When the 
ice was cut away the piers moved back nearly to their original 
positions. This effect was attributed solely to expansion of 



STABILITY OF PIERS. 109 

the ice sheet. The writer's observations during a very severe 
winter at Havre de Grace, on the action of ice formed on the 
Susquehanna River against piers, does not correspond with the 
above estimate of the force of adhesion, and he does not 
understand how the ice can adhere to the pier at all unless 
the water is perfectly still ; any oscillation whatever of the sur- 
face causing alternate rising and falling of the ice-sheet grinds 
and breaks the ice in contact with the surface of the pier, con- 
sequently preventing time for any adhesion to exist. This was 
noticeable on four or five piers at the Susquehanna Bridge ; the 
ice was some 15 inches thick, and remaining for months, with- 
out movement in a horizontal direction, during great changes of 
temperature. It was unsafe to approach the piers too closely, 
that is, within a foot or two. The writer does not question 
the great pressure that would be exerted by the ice on the 
pier while expanding, except in so far as this condition imme- 
diately surrounding the piers would affect the pressure on the 
piers from expansion, as this effect can only appreciably exist 
when the ice sheet has a very great expanse. The sheet at 
the Susquehanna extended between two and three miles in the 
direction of the longer horizontal axis of the pier, but only, of 
course, a short distance, about 500 feet, in the direction of the 
shorter axis. Even, however, assuming a strong adhesion of 
the ice to the masonry of the pier, a wide range of temperature, 
a great expanse of ice in one or more directions, the danger 
arising from expanding ice can be economically avoided by 
cutting narrow channels through the ice parallel to the axis of 

the bridge. . 

233. Secondly, while Moving as a Whole or in Detached 
Masses — The Breaking and Flowing of the Ice at Gray's Ferry, 
Philadelphia, in the Schuylkill River and the Ohio River at sev- 
eral points, and the Drift Gorge on the Tomhgbee River, Ala- 
bama.-ln the Susquehanna at Havre de Grace there is a 
broad stretch of very deep water divided into two channels by 
Watson's Island, extending about 2| miles to a point above at 
Port Deposit, where rocky ledges seem to rise abruptly a 
lar<re part of which is exposed at low water ; this continues for 



IIO A PRACTICAL TREATISE ON FOUNDATIONS. 

miles above, constituting the falls or rapids. Below these the 
current is comparatively slow, hardly perceptible in low water ; 
this water freezes to the depth of two or more feet, and the 
ice rising and falling with the tide, is generally broken -for 
several feet along the shores or around obstructions, such as 
piers, thereby free to move in a body. When the ice breaks 
above in the spring rises, it is brought down by the rapid cur- 
rent, and coming in contact with the solid mass of ice at the 
end of the rapids, it is thrown up and down and sidewise, 
flooding the streets of Port Deposit with water and masses of 
broken ice on one side, and the tow-path of the canal on the 
other side, of the river. Under this immense power the entire 
mass of ice, three or four miles long and more than half a mile 
wide, moves as a whole,— not more than 8 or iofeet, probably, 
— crushing everything, except masonry, in its movement ; this 
seems to relieve the pressure to a great extent, but the rapid 
flow of water under the ice can easily be observed. The ice 
will then remain in this position for some time. 

234. It will have, however, crushed or broken or torn up 
any temporary breakwater made of large numbers of piles, and 
crushed into splinters the timber of the coffer-dams, breaking 
and twisting strong iron bolts and rods two inches in diam- 
eter ; where it has struck the cutwaters of masonry piers, it 
will be split from 50 to 100 feet above the pier, the ice mount- 
ing the pier in great masses. Evidently the broken ice again 
begins to be accumulated at the upper end above and below 
the broken sheet of ice, and commonly believed to reach to the 
bed of the river ; but this can hardly be, as in this case the 
water would flow for some distance over the top of the ice be- 
fore such an immense sheet could adjust itself to the new con- 
ditions, which does not occur. At this time another movement 
takes place, with similar results as before ; and this may continue 
for some time, alternately moving and stopping, the main sheet 
of ice still remaining solid, and in the writer's observation only 
breaking up when the warm weather has simply rotted it. He 
believes, therefore, that the moving force is the action of the 
current upon the large face at the upper end of packed ice both 



STABILITY OF PIERS. Ill 

above and below the main sheet, and that it is a mere ques- 
tion of the ice or the pier giving way. A square-ended pier 
would under such circumstances be put to a severe trial, but a 
good cutwater ploughs through the ice with hardly a tremor, 
aided as it is by the ice rising on the sloping cutwater and 
splitting in almost a straight line. 

235. The moment of this force cannot be accurately or ap- 
proximately estimated ; the strongest kinds of timber frames, 
faced with iron rails, are simply crushed and splintered into 
kindling-wood. 

236. Mr. Weisbach and others give formulae for the amount 
of force exerted ; but the elements of it are unknown, and all 
that can be done is to assume a certain value for the area of 
surface pressed, velocity of current, and some unknown factor 
depending on the shape of the pier, and obtaining a result 
which could have no practical value. 

237. By observing the actual result and determining the re- 
sistance to splitting of the ice for a distance above the pier, we 
will have part of the resistance to the moving force. Much of 
it, however, is taken up by friction of the ice as it moves along 
the shore lines, wider at some and narrower at other parts. The 
writer has therefore simply determined the extent of the force 
on the pier by multiplying the area of the split surface by 10 
tons to the square foot, this figure being simply assumed (it 
may be very far from the correct value, as so much depends 
upon the temperature and the condition of freezing; from some 
actual experiments the tensile strength has been found to vary 
from 140 to 200 pounds per square inch), in order to illustrate 
the manner of arriving at the actual force exerted. 

238. The same may be said of accumulated driftwood, ex- 
cept that there is no means of arriving at the force necessary to 
break through a large mass of drift. This generally occurs in 
those rivers in which the water gets out of its banks and spreads 
■over the country, which is the case in almost all southern rivers, 
many of which rise rapidly in one, two, or three days to the 
height of 40 to 50 feet, collecting, from miles on either side of 
the river, in places, immense amounts of drift, entire trees, 



112 A PRACTICAL TREATISE ON FOUNDATIONS. 

logs, brushwood, etc., which form, on meeting an obstruction,, 
a mattress dam from pier to pier, and to a depth of 10 to 12 
feet, with logs and drift at all conceivable angles, extending 
from bank to bank and covering acres of water above. 

239. In the Tombigbee River this was observed in a thirty- 
five-foot rise, but a timber coffer-dam (around a pivot pier 
built of brick), of verticals and two courses of 3-inch plank held 
down to the crib by 2-inch iron rods, octagonal in plane, well 
braced on the inside, resisted this pressure without springing a 
leak of any consequence. This could not have stood an ice move- 
ment such as above described, though apparently it looked 
equally as formidable, and would not yield. All that could be 
done was to keep a number of men with iron-pointed poles 
standing on the lower end of the drift gradually working piece 
after piece from the mass, and steam-tugs pulling with hawsers 
at the larger and longer pieces ; and occasionally under this 
action it would be so far disentangled that immense masses 
would be carried by the current between the piers. 

240. At the Schuylkill, after a very cold winter, the river 
was frozen solidly over, but owing to the number of bridges 
above, and the sinuosities of the stream, there was little chance 
for a similar movement of the ice to that at the Susquehanna, 
and in the break-up in the spring rise it was simply a rapid 
flow of immense masses of broken ice. This did not gorge to 
any extent ; and though it broke barges loose strongly anchored 
and secured, upsetting some, carrying others off, and this flow 
continuing for several days acting on a square-end coffer-dam 
bolted to cribs, the coffer-dam being 20 or more feet wide and 
12 to 15 feet high, with no masonry built inside, but good 
strong timber bracing being in place, the water rising nearly 
to the top of the dam, no damage was caused to the dam at 
all, did not fill with water, and work proceeded at once. 

241. This dam had no protection of any kind above it, 
whereas the Susquehanna dam of the same construction, though 
double the size, was protected by a number of piles, numbering 
75 or 100, driven close together in the form of a breakwater, 
which was crushed to pieces, and we never saw or heard of the 



W.A TER - WA Y IN CUL VER TS. 1 1 3 

piles afterwards. These piles were not braced rigidly together, 
as it was vainly thought better to allow the piles to gradually 
yield to the pressure, and thereby break the force of the press- 
ure to some extent ; but to no purpose. 

242. In the one case the movement was slow and powerful ; 
in the second no movement of the drift as a whole observable, 
notwithstanding the very great velocity of flow of water ; and 
in the third large masses of broken ice moving with a very 
great velocity, their comparative destructive effects being as 
above described. 

243. The action of the wind upon the piers has been 
explained and illustrated by an example. Experiment proves, 
that its force, either alone or combined with the one above 
discussed, will neither cause ordinary piers to slide nor over- 
turn. The piers of the P., W. & B. bridge at Havre de Grace 
are apparently unusually light, only extending a few feet above 
high-water, and carrying very short spans, giving what might 
be called the minimum elements of resistance to these press- 
ures. These certainly seem safe against such pressures. It 
is true that they are protected by the island just above to a 
considerable extent. 

244. As to the crushing resistance of the masonry under 
the influence of the weight of the pier, the wind, and the ice, 
there is such a wide margin of safety in the strength of the 
stone that no apprehension of this kind need be felt, as in 
practice the greatest pressure that can possibly occur would 
not exceed the mean pressure more than about two times, 
which would give a large factor-of-safety. 

Article XXIII. 
WATER-WAY IN CULVERTS. 

245. In determining the necessary water way for box and 
arch culverts, so many and so varying conditions arise that 
it is impossible to deduce even an approximate formula that 
would be applicable to even a single stream, and on a hundred 
miles of road every ditch and every stream would require a 



114 A PRACTICAL TREATISE ON FOUNDATIONS. 

different coefficient, the value of which could only be wildly- 
guessed at without a survey, the expense of which would be 
many times more than the cost of a culvert much larger than 
actually necessary. The more common formulae are simply 
based on the supposition that the area of the water-way in 
square feet is equal to some root of the drainage area in 
acres multiplied by a constant the value of which is unknown ; 
for instance, area of water-way in square feet 



= C ^drainage area in acres 

(Myers' formula). 

246. Practically no formula is generally used. The engineer 
can generally find in the neighborhood some highway bridge 
which by observation or information obtained from residents 
will serve as a guide ; or in the absence of this, places can be 
found in which the water is confined between the banks of the 
stream in times of the highest flood known in the locality, or 
by taking cross-sections of the stream as indicated by the limits 
of high-water, but here the velocity of discharge would be un- 
known. Altogether we have no data upon which to base in 
the beginning an intelligent opinion, but in general, owing to 
the rapidity of railway construction now, temporary openings 
are left in the way of trestles, which can always be made suffi- 
ciently long to give full water-way, leaving the question of per- 
manent culverts to be settled later. 

247. Good judgment generally determines the proper size 
of culverts. Sometimes a single opening of a foot square built 
of rough stone will carry the necessary water, throwing, over 
and around this, broken stone (before dumping the ordinary 
earth), which would allow any unusual discharge to find its way 
through without any damage to the embankment, or small 
terra-cotta pipes from 6 inches to 1 foot in diameter may be 
used. These would be applicable simply at depressions where 
there are no permanent or well-defined ditches or streams, but 
not where the embankment would dam up the water in case of 
hard rains, which might by seeping through the earth cause 
settlement and possibly danger. 



ARCH CULVERTS. 115 

248. For any well-defined ditch or stream a culvert 2 feet 
square, increasing to 3 or 4 feet wide by 5 feet high, as the cir- 
cumstances seem to require, will answer every purpose. If a 
larger water-way is required use the double box of correspond- 
ing dimensions, and if this is not sufficient the arch culvert 
should be used. The side walls vary in thickness from 2 to 3 
feet according to height, and covering stones from 10 to 16 
inches thick, according to the length of the span. 

249. The vitrified terra-cotta pipes used are what are known 
as double-strength glazed pipe. They are now comparatively 
cheap, costing at most from twenty cents to one dollar per 
foot, according to size, and easy to handle ; but there is always 
more or less danger of cracking or breaking, and for this reason, 
if no other, masonry culverts are preferred. These cost from 
two to five dollars per foot of length, depending upon conveni- 
ence of material and kind of work required. 

250. Cast-iron pipes have been used extensively in some 
sections of the country in diameters as great as 4 feet and in 
lengths that may be required. These cost from one to eight 
dollars per lineal foot, according to their weight. Special care 
Is required in laying these pipes to prevent undue settling. 



Article XXIV. 

ARCH CULVERTS. 

251. WHEN a larger water-way is required than the limit of 
box culverts, say 4 feet span, arch culverts are constructed. 
These differ only in the size from ordinary arches, which have 
been fully discussed, except that the spaces between the abut- 
ments are generally paved, and an apron wall is built from side 
to side at the ends of the arch of a depth somewhat greater 
than the foundation bed of the side walls or abutments, the 
paving also extending above and below between the wing walls. 

252. The usual manner of connecting the wing walls with 
the head walls is to throw them well back from the arch ring 
and then build them to the proper height with the usual batter, 



116 A PRACTICAL TREATISE ON FOUNDATIONS. 

and thickness proportioned as in retaining-walls, the angle 
of the wing being determined by circumstances — generally 
not more than 30 degrees with the axis of the arch. The only 
objection to these are the square shoulders presented at the 
entrance of the arch, forming a lodgment for ice and drift. 
This can be avoided to some extent by starting the wing wall 
at the front of the abutment, and carrying it up vertically to the 
springing line, and then commence the batter wall either at the 
springing line of the soffit, or leaving an offset at the springing 
line equal to the thickness of the arch ring and commencing 
the batter wall at the back or extrados of the arch ring. This 
was the plan adopted in the Philadelphia extension of the B. 
& O. Ky.. except that the wing wall to the height of the spring- 
ing line was carried up on a warped or twisted surface, that is, 
vertical where it adjoined the abutment, but assuming a gradu- 
ally increasing batter to the end of the wing. This presents 
no shoulder to the height of the springing line, but presents 
shoulders above that line. It allows the wing wall to be bonded 
for its entire height into the head wall. 

253. For any very small arch from 5 to 15 feet span they are 
generally full-centre circular arches. For spans from 20 to 30 
feet the segmental arches offer some advantages : for the same 
length of mtrados give a little longer span and the area of the 
water-way is a little greater, and for the same length of span 
there is a little less masonry, and does not require so great a 
rise, which is often an important consideration. On the con- 
trary, the segmental arch requires greater thickness of arch ring 
and abutments. 

254. Sometimes the wing walls are perpendicular to the 
axis of the arch, or in other words a simple extension of the 
head walls in a straight line ; these offer no advantages, and 
are not used in any but very small arches. 

255. Formula for the thickness of the arch ring have already 
been given. An arch ring somewhat thicker, both for circular 
and segmental arches, is advisable : the cost will not be much, 
if any, more, and presents a better and stronger appearance. 

256. Trautwine gives the following rule for determining 



ARCH CULVERTS. II? 

the thickness of abutments for arches in feet at the springing 
line, for any abutment the height of which does not exceed 
\\ times the thickness at the base. Thickness of abutment 
at springing equal to 

radius in feet , rise in feet , , 
5 10 

The radius in this formula is that of a circle passing through 
the two springing lines and the crown, on the soffit. As it is 
always practicable to find a circumference passing through 
any three points in the same plane, this formula is applicable 
to a semicircular, a segmental, or elliptical arch. Laying off 
this distance and the height of the wall perpendicular to it, 
and at the bottom of this line drawing another line from one 
half to two thirds of the height, the line closing this quadrilat- 
eral would represent the surface of the back of the wall. This 
thickness is given to resist the thrust on the wall arising from 
the earth pressure of the embankment of any height over and 
around the wall. This does not take into consideration the 
thrust on the abutment by the arch, which is in the opposite 
direction to the earth pressure and at least neutralizes it in 
part, nor any support arising from the wing walls. This will 
no doubt give sufficient thickness in any case, but to resist the 
effects of the rolling load it is supposed that the earth has been 
deposited behind the abutments. 

257. Applying this formula to spans 6', 10', 16', with a rise 
of one sixth of the span, segmental arch, in the first case the 
radius equal to 5, in the second equal to 8.2, and in the third 
equal to 13.2. 

The rise in feet would be, respectively, = 1, in the second 
= 1.7, and in the third = 2.7. Thickness (Trautwine's for- 
mula) of abutment at top in feet = 3.r, in the second = 3.8, 
and in the third = 4.92. Actual thickness of abutment at top 
in feet in same cases = 3.3, in the second = 4.6, and in the 
third = 5.6. 

Actual depth of key-stone at crown = i.ofoot, in the second 



Il8 A PRACTICAL TREATISE ON FOUNDATIONS. 

= 1.3 feet, and in the third = 1.6 feet. For semicircular 
spans, as above, actual depth of key-stone at the crown = 0.6a 
foot, in the second = 1.0 foot, and in the third = 1.2 feet. 
Actual thickness of abutment at top = 3.0 feet, in the second 
= 3.6 feet, and in the third = 4.6 feet. 

Trautwine's results agree very closely with those in actual 
use for a semicircular or full centre arch, but smaller than the 
practice for segmental or elliptical arches. The practical rule 
is to add one third part additional in these cases, but this 
would be considerably in excess of the actual thickness of 
abutments given in the table above. 

258. But, as stated before, the best rule is to extend the 
line of pressure from the top to the bottom of the abutment, 
and if this line remains in the middle third of its thickness, it 
will be stable so far as the thrust of the arch is concerned, and 
determine its stability against the earth pressure by the em- 
pirical rules for the thickness of retaining-walls ; the least 
thickness thus determined will certainly be ample, as the two- 
pressures balance each other in part. 

259. But the earth pressure is hard even to approximate, 
as evidently the condition would be that of a surcharged wall ; 
for by removing the arch ring and the earth above it the 
abutment would simply be a foot wall at the bottom of a mass 
of earth sloping away from the top of the wall at the angle of 
repose, either resulting from the removal of the earth to that 
slope or allowing it to assume its natural slope. At the solu- 
tion of this the wonderful penetration of Mr. Rankine seems 
to falter, but he suggests the following : 



*" a/ W ' X r . 

— = cos (p V > — X — ; — --- + 2c -T- {x + 2c\ 

x ogw i-fsin0 ' ' 

in which t" = the thickness of the surcharged wall, c = height 
of surcharge, x = height of wall, <t> = angle of repose of ma- 
terial, w' = weight of a cubic foot of the earth, w = weight of 
a cubic foot of the masonry in the wall. Mr. Trautwine gives 
the formula as follows : True theoretical thickness = weight of 
earth X 0.643, in which the weight of the earth is that of a 



ARCH CULVERTS. II9 

triangular prism, whose base is formed by the height of the 
wall, the prolongation of the plane of maximum pressure to its 
intersection with the slope of the ground, thence by the length 
of this slope to the top of the wall. The moment of this 
equated to the moment of the weight of the wall will enable 
us to determine the thickness as in retaining-walls. 

260. With a surcharge two times the height of the wall, he 
gives the following as safe thickness: cut stone 0.58, rubble or 
brick 0.63, of the height of the wall ; and for a surcharge nine 
times the height of the wall, cut stone 0.65, rubble or brick 
O.80, of the height of the wall. These thicknesses are roughly 
one and one half times of those when the earth is level with 
the top of the wall. 

261. Whether these are right or wrong, they have but 
little bearing in the case of the abutments of the arch ; for if 
the earth, as is often the case in railroad abutments, and 
which is the general case for culverts under highway bridges, 
only extends a few feet above the top of the arch, it evidently 
would be considered safe to consider the half arch, with its 
abutment and weight above, as the equivalent of a vertical- 
faced wall of the height of the embankment, and find the 
thickness of the wall to insure stability, as in retaining-walls, 
or using the thickness followed in practice, that is, from two 
fifths to one half the height. Take, for example, a semi- 
circular arch of 20 feet span, the rise 10 feet -f- arch ring 
-j- spandrel = say to 15 feet, and height of abutment between 
footing-courses and springing line 10 feet, the equivalent verti- 
cal-faced wall would then be 25 feet, and two fifths of this would 
be 10 feet = required thickness, or one half the height would be 
12^ feet. This would evidently be ample. Mr. Trautwine's 
rule for the thickness of abutments would give 5 feet at top 
and 6.6 at base. 

262. The writer does not believe that any greater height of 
embankment, no matter how high, would require any greater 
thickness of abutment wall, and even doubts if the pressure 
would be any greater ; but if it is, the greater stability of the 
wall, resulting from increase of weight of material above, 



120 A PRACTICAL TREATISE ON FOUNDATIONS. 

would at least balance the increased thrust. The abutment 
would only give way by sliding or crushing, as the arch as a 
whole would be stable against overturning on account of the 
balanced pressure from the two sides. 

263. It is not uncommon to see little foot walls supporting 
as it were sloping embankments ten times their own height, 
even when the material would continue to cave and slide 
down. It is true that these walls are always made of thick- 
nesses equal to their heights, or even greater. 

264. In these calculations neither the adhesion of the mate- 
rial, nor the support that the earth gives to itself by a tendency 
to be self-supporting by arching itself above the arch, nor the 
adhesion or cohesion of the mortar in the masonry, is con- 
sidered. 

265. If the above reasoning is not true, the linings of tun- 
nels would be ridiculously thin, being only a few bricks in thick- 
ness, say from two to three feet, or from 5 to 8 rings of brick 
laid flatwise. It is true that such linings would not hold the 
pressure if it should once take a move, but are ample to prevent 
any movement. Conditions are of course different under a 
bank of loose earth thrown up, even after the lapse of time. 

Article XXV. 
THE COST OF WORK. 

266. It is considered by some useless to give the cost of 
any particular kind of work, as this depends upon so many con- 
tingencies and these varying rapidly from year to year, depend- 
ing upon the abundance or scarcity of materials, the amount of 
work being carried on, the character of the specifications, the 
scarcity or abundance of labor, the time in which the work is 
to be completed, as well as the amount of work to be done 
at any one time and place : all of these things render anything 
but an approximation to the cost uncertain. It, however, 
serves as a guide. It can be stated as a general principle, that 
it will generally prove economical in the end to pay fair prices 
to responsible parties, and not to endeavor to get work done 
at a price less than it is really worth, and thereby secure only 



THE COST OF WORK. 121 

irresponsible contractors, who will not only execute the work 
badly, will never execute it in the specified time, will give all 
kinds of trouble, will endeavor to impose on you by numerous 
extra bills, by enormous charges for extra work, but too 
often, after performing that part of the work in which the 
greatest profit exists, abandon the work, leaving large unpaid 
bills for material and labor to be paid by the company, and a 
larger cost to complete the remaining work, than would have 
been really required to do the entire work, if let to capable 
and responsible men. Almost all important work is done by 
contract, because it is the cheaper in the long-run. 

267. Ordinary brick or stone masonry, concrete and earth- 
work, are generally paid for by the cubic yard. Brickwork for 
the walls of houses either by the cubic yard or by the perch or 
face measure, for walls of definite thickness, say one and one 
half brick or 12 inches ; if the wall is two times one and one half 
bricks, the area of the surface is doubled ; if only one brick thick, 
then two thirds of the surface is taken. All openings are some- 
times included, sometimes omitted, and sometimes averaged — 
either according to custom or agreement, or sometimes by the 
1000 brick, allowing so many to the cubic yard — about 500. The 
best dressed work, such as coping, cutwaters, or raising stones, 
is paid for either by the cubic yard or the cubic foot. Frame 
timber is generally paid for by the 1000 feet B.M. ; B.M. mean- 
ing board measure. The unit being foot B.M., that is, a plank 
12 inches long, 12 inches wide, and 1 inch thick, a stick of timber 
15 feet long, 12 inches broad, and 10 inches thick would then 
contain 1 50 feet B.M. Cross-ties are paid for at so much apiece. 
Piles are generally paid for by the lineal foot, either for the 
ordered length, or for that portion left in the work, and allow- 
ing so much for the cut-off in addition. 

268. Trestle-work is sometimes paid for at so much the 
running foot of a completed trestle. This, in many respects, 
is the most satisfactory mode of estimating. Iron, whether as 
bolts, rods, cylinders, and screw-piles, so much by the pound, 
and, in case of screw-piles and cylinders, so much for each foot 
sunk below water or the bed of the river. 



122 A PRACTICAL TREATISE ON FOUNDATIONS. 

269. In sinking caissons, so much per cubic foot of material 
moved, estimated by multiplying the bottom area by the dis- 
tance from the surface of the water or the bed of the river to 
the lowest point reached by the caisson, or the lowest point of 
the foundation bed. 

270. Again, all of these separate items on any work may be 
paid for in a lump sum. The contractor is likely to get the 
best of this, as he will be pretty sure to make a liberal allowance 
for contingencies ; and if the estimate is anyways doubtful, it is 
a great temptation to do poor work, and if any loss occurs, the 
company will in general make it good, thereby making the 
work cost more than was anticipated. 

271. A responsible party who gives a reasonable bid is in 
general the safest to accept ; the highest bidders do not want 
the work very much, and the lowest want it too much. 

272. Stone-cutting is paid for sometimes by the actual 
number of square feet cut, or simply by the face measurement 
of the stone ; the finest dressing by the day, or by the actual 
surface cut. 

273. However the work may be done, the contract should 
be clear and distinct, and full as to all essential conditions and 
requirements, avoiding at the same time useless and onerous 
conditions in regard to minor details, which are never carried 
out, and only give excuse for adding a good percentage to the 
profit arising legitimately from the work. Say in the specifica- 
tions what you mean and mean what you say. 

274. Contractors are generally required to furnish all mate- 
rials — tools, derricks, engines, boilers, and everything, called 
the plant — necessary to carry on the work properly and expe- 
ditiously. Poor contractors will furnish broken-down carts and 
mules, worn-out boilers, engines, and pumps, barrows and 
tools in dilapidated condition, and all often in insufficient 
quantities, causing loss of money and time to both contractor 
and company. The company should always reserve the right 
to supply the deficiencies, if any exist, at the contractor's ex- 
pense. 



THE COST OF WORK. 12% 



Article XXVI. 

THE COST OF MASONRY AND CONCRETE. 

275. THE following is the actual cost of masonry, concrete* 
etc., in some important works in the writer's experience : 

Per 

Cubic Yard. 

Granite piers, not including cement, 13,767 cubic yards % 13 00 

«• " not including cement, second-class masonry 10 00 

*' pedestals, not including cement, first-class masonry 13 oo 

Limestone piers, first-class masonry, not including cement, 5652 cubic 

yards I2 °° 

Limestone abutments, second-class masonry 8 oo< 

" coping 15 °° 

Granite arch stone ID °° 

Brick in walls of houses, including mortar, $11.00 per 1000 7 00 

Brick arch ring < 9 °° 

Sandstone piers, cement included, about 2000 cubic yards 11 00 

«« " " " "10,000 " " 14 3° 

Retaining-wall, rubble, not including cement 4 5° 

Brick wall piers, 2000 cubic yards 15 00 

Concrete in cribs, not including cement, 18,146 cubic yards 6 00 

" in interior of caissons, not including cement,6o36 cubic yards 1500- 

j n << tc U it « " j 500 <« << J 3 OO 

Box-culvert masonry 4 5° 

Paving ■ 2 75 

In the above table the cost of granite and limestone and 
sandstone piers included all coping and cutwater stone, and 
also the cement in the sandstone piers ; in the granite and lime- 
stone piers the cement was furnished by the railroad company.. 
The sandstone in large part was hauled over 100 miles by raiL 
Sandstone piers in the same bridge built of local stone, with a 
fair profit to the contractor, only cost $10.00 per cubic yard. 
$12.00, instead of $14.30, would have been a good price for the 
work, and could have been done at that figure ; but the presi- 
dent of the road preferred one contractor at $14.30 to another 
equally as good, in the writer's opinion, at $12.00. In the 



124 A PRACTICAL TREATISE ON FOUhWATIONS. 

25,682 cubic yards of concrete as above there was used about 
24,230 barrels cement ; the average cost of this was $2.08 per 
barrel. About two thirds of this was Portland cement, of Alsens, 
London, and Saylor's American brand ; these cost, respec- 
tively, $2.75, $2.80, and $2.50 per barrel. The Hoffman and 
Norton Rosendale cost about $1.29, delivered on the work. 

In the above table the price of brick in piers costing $15.00 
per cubic yard was caused by the fact that brick were very 
scarce and difficult to get, and had to be transported on barges 
for a long distance up a very rapid river, and could only be 
transported during the rises in the water. Under ordinary 
circumstances $8.00 per cubic yard would have been ample. 
The box culvert masonry is higher than usual, owing to small 
quantities and long haul. The paving should not usually cost 
more than $2.00, but good paving, which is set edgewise 
and properly laid, with the care necessary to avoid any undue 
deflection or obstruction to the current, is worth a fair price, as 
to some extent it may have to act as an inverted arch. It is 
well to fill the interstices between the stones with gravel, chips 
of stone, or even sand, as it will prevent undermining. The 
flow of the stream itself is likely to do this filling during the 
rises in the stream. Careless paving is worth but little, and 
owing to its supposed want of importance is often hardly 
worthy of the name. It should be at least from 10 to 12 
inches thick, and should be laid slightly concave on top, the 
edges a little higher than the centre. It is well also for this 
paving to extend well beyond the apron walls, or even to the 
end of the wings. It should never be placed under the abut- 
ment or wing walls, but between and abutting against them 
well above the bed. 

Cost of Quarrying, Dressing, Laying, Finishing, and 
all Tools, Machinery, and Materials. 

276. Cost of quarrying varies greatly with the kind of stone, 
the condition of the quarry, cost of labor, distance of quarry, 
but may be roughly estimated. 



THE COST OF WORK, 12$ 

Granite. Sandstone. 

Good size stone for rubble $1.00 per cu. yd.; $0.50 

Good size ashlar stone $4.00 " " $3-°o 

Dressing beds and joints $0.30 " sq.ft.; $0.15 

Cement and sand $1.00 to $0.50 per cu. yd.; $1.00 to $0. so- 
Laying $2.50 to $1.75 " " $2.50 to $1.75 

Hauling depending on distance $1.00 to $2.00 " " $1.00 to $2.00 

At the above rate a cubic yard of face or dressed stone 
would cost in the pier for granite $18.00 per yard, assuming 35 
square feet of dressed surface. The backing would cost the 
same as the above, less the cutting, but allowing $1.00 for ham- 
mering and $1.00 for the mortar, or $8.50. In a pier containing- 
1500 cubic yards, one third would be cut stone and two thirds 
backing. Actual cost per cubic yard would be $11.60, pro- 
vided the cement was furnished by the company, which is 
a good plan in many respects, but is apt to lead to a liberal 
use of cement ; but the satisfaction is that you will insure better 
cement and better work. 

277. The writer in this calculation assumed a stone 6 ft. 
X 2\ ft. X 2 ft. just making one cubic yard, and assumed the 
beds and joints to be cut true throughout, the face left rough. 
Stones of this size are rarely of such perfect shape. The joints 
of the stones are not cut true more than from 1 to \\ feet from 
' the surface. The upper bed is not required to be cut with the 
same nicety and care as the lower bed, and it is far better to be 
rigid in regard to the lower bed and allow if necessary the 
upper bed to be a little rougher towards the back or the tail of 
the stone, for by this means you insure solid work and avoid 
to a large extent cheating, consequently bad work somewhere 
in the structure ; in this way you may save three or four 
square feet of dressing, which is equivalent to from 90 cents to. 
$1.20 per cubic yard, or the actual cost of the work will not 
exceed $10.50 per cubic yard, and for $12.60 should allow 20. 
per cent profit to the contractor. Good first-class granite 
piers can be built for at most $13.00 per cubic yard. The 
cost of first-class sandstone ashlar would be on the same 
basis of calculation $9.50 per cubic yard. The actual cost. 



126 A PRACTICAL TREATISE ON FOUNDATIONS. 

would be $7.90 and allowing 20 per cent profit to contractor, 
or $9.48 per cubic yard of masonry in the pier. Limestone 
masonry would not materially differ in cost from that of sand- 
stone. 

278. Good brick-work in walls of buildings can be con- 
structed for $7.00 per cubic yard, and from $10.00 to $13.00 
per 1000. In tunnels, from $8.00 to $9.00. First-class masonry, 
$10.00 to $12.00. Second-class masonry or brick-work for arches, 
$8.50. Box-culvert masonry, from $2.00 to $5.00. Concrete from 
$4.00 to $8.00, varying largely in proportion to the kind of 
cement used and proportions of sand and cement, and nature 
the of broken stone used. Rubble, from $3.50 to $5.00. 
Paving, from $1.00 to $2.00. Sand will cost, according to qual- 
ity and length of haul, quantity, etc., from 20 cents to $1.00. 
■Cement, ordinary, in barrels, from $1.00 to $1.25 per barrel ; in 
bags, about 10 cents less, say 90 cents to $1.1 5. Portland cement, 
from $2.00 to $3.00 per barrel. Brick cost from $6.00 to $8.00 
per 1000 brick, according to quality and demand. 

Article XXVII. 
DIMENSIONS OF PIERS. 

279. The following are some of the dimensions arid forms 
of piers and abutments constructed by the writer : 

The Susquehanna River bridge was about 6200 feet long, 
arranged as follows: 2 spans, 1 through and 1 deck, 520 feet ; 4 
deck spans 480 feet, 2 through spans 375 feet, 1 deck span 200 
feet. There were eleven piers and two abutments. Six of 
these piers were in water and five on land. Of those in water 
five rested on pneumatic caissons sunk from 60 to 90 feet below 
the water surface ; one built inside a coffer-dam ; all founded on 
rock, except two, which rested on beds of large bowlders mixed 
with gravel and sand about 70 feet below water surface. The 
masonry commenced on the crib at varying depths below the 
water surface, and was built up in steps or offsets to a point 
.about 4 feet below low-water, at which level the neat work com- 



DIMENSIONS OF PIERS. 12.^ 

menced, and was carried up to the proper heights above high- 
water, which for the piers carrying the 5 20-foot spans were 90 feet, 
and for the others or deck spans the tops of the piers were lower 
by the depth of the truss, from 40 to 50 feet. The piers were 
generally under coping 32 feet long and 10 feet wide for the low 
piers, and 35 feet long and 11 feet wide for the four high piers 
carrying the through spans. The batter was \ inch to the vertical 
foot from the top to the footing-courses on both sides and lower 
end. On the upper end, about 12 to 15 feet above low-water, a 
cutwater commenced, sloping downwards at an angle of 45 
degrees, so that the cross-section of the pier at the top of the 
footing-courses would be about 20 feet by 61 feet long, to which 
the offsets would add about 10 feet all round. With the excep- 
tion of the upper end of these piers to the top of the cutwater, 
these piers were square-ended from the bottom to the top. 
The cutwater was finished with a blunt triangular end. The 
coping and the triangular ends were cut to a smooth surface; 
the other parts of the piers were first-class ashlar masonry, rock 
face, with pitch line on the joints or edges of the stones. All 
of these piers had large raising stones on top of the coping 
6 ft. X 6 ft. X 22 in. See Plate XIX, Figs. 1 and 2. 

280. There was in addition about 2300 linear feet of iron 
viaduct divided into 30-foot spans requiring about 154 pedestals 
reaching only a few feet above the surface of the ground. The 
pedestals were 3^ feet square under coping ; coping-stone 4 
feet square and 15 inches thick, projecting 3 inches over shaft, 
the trestle being from 40 to 60 feet high. 

281. The total cost of this bridge was $1,737,266, as follows : 
Foundations, $469,066; masonry, $208,000; superstructure, 
$1,060,200 ; and it was completed in two years from the time of 
letting contract. All things considered, it can be considered as 
executed both economically and expeditiously. All masonry 
was constructed of granite obtained from quarries a few miles 
above the site of the bridge. The raising stones were brought 
from near Wilmington, Del., as stones of the size required 
could not be obtained from the other quarry ; and in addition 
the Port Deposit granite had certain seams crossing the natu- 



128 A PRACTICAL TREATISE ON FOUNDATIONS. 

ral beds, which rendered it uncertain for such heavy concen- 
trated loads. The total quantities of materials used in this 
bridge, exclusive of superstructure, were as follows : 

282. TABLE OF QUANTITIES AND COSTS. 

Timber in caissons, cribs, and 

coffer-dams 2,727,755 ft. B.M. @ $46.80 = $127,658.93, 

Iron in caissons, cribs, and coffer- 
dams: 

Screw bolts 124,306 lbs. 0.06 7,45S;36 

Drift " 216,028 "■ 0.05 10,801.40 

Spikes 44,650" o.osi 2,455.75 

Cast washers 15,206 " 0.02^ 323.13 

Total concrete in air-chamber and in 

excavations below cutting edge 4,036 cu. yds. 15.00 60,537.45 

Total concrete in cribs and under 

piers 11,141 " 6.00 66,846.00 

Excavation, sinking caisson to cut- 
ting edge 781,934 cu. ft. 0.20 156,386.80 

Excavation, sinking caisson below 

cutting edge 34,452 " 0.20 6,890.40 

No. of bbls. Portland cement 10,620 bbls. 2.80 29,736.00 

" " " Rosendale and Cum- 
berland cement 3,668 " 1.29 4,731.72 

Total for foundations $473,825.94 

" " Masonry, first-class 14,582.80 cu. yds. 13.00 $189,576.40 

" pedestal masonry, first-class. 429.53 " 13.00 5,583.99 

" for masonry, second-class.. . . 817.00 " 10.00 8,170.00 

" rubble masonry and concrete. 1,314.61 " 6.00 7,887.66 

" for substructure $685,043.89 

Coffer-dam for pier 5, estimated .... 5,000.00 

Cement in masonry and concrete. . 8,700 bbls. 1.29 11,143.00 

Cost of engineering, approximate 20,000.00 

Extra bills handling material, extra 

work, etc., estimated 20,000.00 

$741,186.89, 

This includes some items not included in paragraph 281. 

283. To determine the cost per cubic yard of the volume 
whose base is the area of the bottom of the caisson and whose 
height is the depth sunk, which is the most convenient form 
for arriving at an approximate estimate of the probable cost 



DIMENSIONS OF PIERS. 



129 



of any proposed structure of this kind, we will take each cais- 
son separately, as all the distances sunk differ, and also the 
dimensions of the caissons. We have then the following for 
the above structure : 



Caisson No. 2. , 



9.. 



Dimensions 


Area in 


Depth 


Volume 


Volume 


Cost 


at Bottom. 


sq. ft. 
















cu. ft. 


cu. yds. 


cu. yd. 


63.27X25.93 




68.32 


112,124 


4153 


$15.08 


67.27X25.93 




70.72 
65.25 


123,402 


4571 


15-25 


79.40X32-85 




59-9' 

88.4 


159,588 


59" 


I5-03 


70.85X32.6l 




76.00 
78.26 


189,578 


7021 


15-56 


78.19X42.27 




65.01 


231,692 


S581 


16.17 


30237 


15.50 



Total Cost, 

162,613.41 
69,603.92 

88,830.64 

109,248.70 

138,769.42 



469,066.09 



The total cost in this table should agree exactly with the 
corresponding item in preceding table, viz., $473,825.94; but in 
the above table the concrete is calculated by averaging the cost 
of cement, and in addition there is some 200 yds. of concrete 
under one of the piers not included in the caissons proper. The 
iron is also taken at an average price in the above. The above 
table is, however, a close approximation to the actual costs. 
If the displacement is measured from the bed of the river and 
not from the water surface, the average cost per cubic yard on 
the above unit prices would be considerably greater than the 
above. As for example, in caisson No. 2 the displacement would 
be only 94,504 cu. ft. instead of 1 12,124 cu. ft., and 3500 cu. yds. 
instead of 4153 cu. yds., making the cost per cubic yard $17.89 
instead of $1 5.08 per cubic yard. These would depend upon the 
terms of the contract. In this bridge the excavation or dis- 
placement was measured from the water surface. Mr. Baker 
in his work makes this $19.93 per cubic yard, and the average for 
the entire work $22.69, instead of $1 5.50, as in table. The above 
quantities and costs are taken from the writer's final estimates 
on the work. In caissons 4, 8, and 9 the actual depths to the 
bottom of the cutting edges are respectively, 59.9, 76.00, 65.01 ; 



I30 A PRACTICAL TREATISE ON FOUNDATIONS. 

whereas to the lowest point of rock the depths are, respec- 
tively, 65.25, 88.4, and 78.26. In these caissons the cutting edges 
rested on rock at one end, and were, respectively, 5.35, 12.4, and 
13.25 above rock at the other. This will again be referred to 
in discussing pneumatic caissons. 



THE SCHUYLKILL RIVER BRIDGE, B. & O. RY. 

284. This bridge, located near Gray's Ferry, Philadelphia, 
was comparatively short and low, requiring a drawbridge. 
There were two abutments, three piers, and one pivot pier. 
The spans were comparatively short, being as follows : One 
span 201 ft.; draw-span 242.64 end to end, 75 ft. clear opening 
at low-water; one span 200 ft., one span 152 ft. The line 
crossed the river at an angle of 53 15' with the direction of 
the current, requiring the piers and abutments to be very long 
in proportion to the length of the span. The east abutment, 
U-shaped in plan, was founded on rock only a few feet below 
the surface of the ground. Pier No. 5 was located on the edge 
of a rapidly dipping rock, and was built inside of a coffer-dam ; 
the rock on the east side was exposed at low-water, and on the 
west side was from 10 to 15 ft. below the water surface. The 
range of the tide was from 5 to 10 ft. An ordinary coffer-dam 
was first tried, but owing to the great difference of the depth 
on the two sides of the dam, and the silty nature of the material 
overlaying the rock on one side, and no material on the other, 
this dam failed : a good crib-dam would have stood, but on 
such a sloping surface it would have been difficult to frame 
and handle. After the failure of the first dam, a contract was 
made with Mr. J. E. Roninson to put in his patent coffer-dam 
(this will be explained under Coffer-dams), and after much 
delay and many breaks we finally reached the rock. The 
remaining piers, 2, 3, and 4, rested on pneumatic caissons sunk 
to the rock. The west abutment, U-shape in plan, rested on a 
pneumatic caisson. The following is a table of quantities and 
.costs : 



DIMENSIONS OF PIERS. 



131 



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2 o w 



«n g, 



X X 



u 


xss 


b 


^-3 E 

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°--Q 



co£ 



o a 



2 >- 

? rt — 

bo s c 

4-> bO t) 

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132 A PRACTICAL TREATISE ON FOUNDATIONS. 

285. In the above table the price for timber is taken at 
$40.00 per 1000 B.M. This is an average of the prices. The 
actual contract price was $45.00 for timber in caissons, $38.00 
in cribs and coffer-dams, and $35.00 for timber in open caissons 
sunk on top of piles for the guard piers. The cost of iron is 
also an average for the different grades. Taking the four 
pneumatic caissons, exclusive of the masonry, the cost would be 
$239,047— $34,364+cement $748q=$2 12, 172.26. The total dis- 
placement in cubic yards is 14,764 ; we find that $212,172.26 -f- 
14,764 = $14.40, which is the cost per cubic yard under the 
water surface. This is generally the basis upon which the con- 
tract for piers is determined. In the above case if the excava- 
tion or displacement is taken from the mud line the cost would 
be about $18.00 per cubic yard. It is always better to make the 
water surface the starting point, as in all cases the low-water sur- 
face can be definitely ascertained or agreed upon, marked, and 
preserved as a datum. The bed of the river may fill up or scour 
out, and the datum will be uncertain and cause confusion and 
uncertainty. The timber used in these caissons was entirely 
of yellow pine. The masonry was of a tough limestone, easily 
splitting in one direction, but very difficult to split in the other. 
The pivot pier was 33 ft. in diameter under coping, 35 ft. at 
bottom of shaft, two offset courses, and 38 ft. at bottom of 
offset courses. The coping was 16 in. thick. The other 
dimensions in the table are given under the coping and at the 
bottom of offset courses. 

OHIO RIVER BRIDGE, POINT PLEASANT, W. VA. 

286. From bank to bank on this river was 1 370 feet, divided 
into five spans, respectively 250, 250, 250, 420, and 200 feet, by 
six piers, two on land and four in the water. For the land 
piers pits were dug about 15 feet deep, and piles driven 
in the bottom, 2^ feet centres, cut off about 1 foot above the 
bottom, then capped with 12X12 inch pine, the intervening 
spaces filled with concrete ; this was then covered with a solid 
flooring of 12 X 12 inches, upon which the masonry com- 



DIMENSIONS OF PIERS. 



133 



menced ; concrete was piled up all around from the bottom 
to a point about 3 feet on the masonry. For the four river 
piers ordinary coffer-dams were constructed, and on the inside 
of these a timber crib was sunk. This work was prosecuted 
with great vigor and in the face of many difficulties, such as 
floods, intensely cold weather, and a suspension of the work 
for about six weeks during the lowest water and most favor- 
able weather. The average depth excavated below the bed of 
the river was from 10 to 12 feet, through gravel and sand. 
The dams were strong enough to stand a rise of 15 feet, or a 
total pressure due from 25 or 30 feet. All of the foundations 
were completed, and in addition all the masonry of the piers, 
within 12 months from time of commencing, and a consider- 
able number of the pedestals for the iron viaduct were also 
completed. 

287. The iron viaduct was 2380 lineal feet, and of a height 
varying from 60 feet to 20 feet. The grade on the iron trestle 
was \\ feet in 100 on both sides of the river. The bridge 
itself was constructed on a 0.5 grade on the east and 0.25 on 
the west of the channel span. These piers were built entirely 
of sandstone, mainly from the Hocking Valley quarries, a 
hundred miles distant by rail, and partly from a local quarry, 
called Miller's Quarry. The following table gives the crushing 
strength of true cubes, 2X2X2 inches, using in the crushing 



Location of Qu?rry. 



Hocking Valley, No. 1 



Miller's Quarry " 1. 

" 2. 



Slight Signs of 
Yielding at Press- 
ure per cube ; 
per square inch. 



800 or i, 200 

526 " 5,831^ 
650 " 1,662! 
130 " 2,032! 

620 " 4,405 
740 " 4,685 



Crushed or Split 



Pres 

pr.cube 
in lbs 



18,458 

27,885 
12,000 
r 5.93° 
17,620 

18,740 

14,942 
15,442 



Pres. pr. 

s<j. in. 
in lbs. 



4,614 
6,971 



3,982 
4.405 

4.685 

3,735 
3,860 



j Without violence or 

I noise. 
Slight noise. 
Not crushed. 

j Crushed suddenly, 
I without noise. 
( No evidence of yield- 
| ing whatever. 



134 A PRACTICAL TREATISE ON FOUNDATIONS. 

soft white-pine cushions. These cubes were dressed true in a. 
marble yard. 

The writer tested these specimens with the above results, 
and also many other specimens from various places; the 
general average was the same as above. The piers were built 
of the above stone. The tests were made at the Ohio State 
University, Columbus. These specimens were all compara- 
tively fresh from the quarries, as we could not wait very long 
before deciding upon the quarry. The specimens would 
doubtlessly have resisted a higher pressure after seasoning 
thoroughly. Pasteboard cushions are now recommended as 
better than pine. The following are the quantities and costs : 

273,210 feet B.M. pine timber in coffer-dams, cribs, and foundations under piers- 
244,412 " " oak " " " " main and sheet piling. 
3,597 " " poplar " " " " sheet piling. 
13,571 lineal feet of piles in foundations and coffer-dams. 
3,499 cubic yards excavation sand and gravel. 
649 " " concrete in foundations. 
997 rip-rap stone. 

Total cost of foundations $64,652 6£ 

Masonry in piers, first-class, 8,654 cubic yards, $14.30 123,756 92 

Masonry in pedestals, " " 1,224 I4-30 15,91200 

Earth in approaches, 39,-490 " " -22 8,68780 

" " pedestal foundations 2,304 02 

371,962 feet B.M. in trestle approach, $30 per 1000 feet B.M 11,158 86 

11,965 wrought-iron screw and drift bolts, 5 cts 59S 25 

7,939 cast-iron washers and packing spools, 4 cts 317 56- 

Extra bills 174 64 

Total cost of substructure and approaches, exclusive of iron viaduct $227,562 67 

Total cost of bridge proper, 1370 lineal feet, $126.50 173,213 00 

" " " iron viaduct, 2380 " " 39.00 92,771 00 

Total cost of completed structure $493,546 67 

288. The dimensions of piers and pedestals were as fol- 
lows : Pier No. 1, carrying one end of one span 250 feet 
and end of iron viaduct, at top 22.22 X 6.5 feet, at bottom 
25.54 X 10.04 feet, 43.84 feet high. Offset course 4.65 feet, 
height, and 28.53 X 12.53 f eet at bottom, total height 48.49 feet, 



DIMENSIONS OF PIERS. 1 35 

square ends. Piers 2 and 3, carrying 250-feet spans, top 23.00 
X 9.00 feet, square ends, at 33.35 feet from top, 25.8 X 1 1.8 ft. 
Belt-course 2 feet thick, 38.92 X 13.22 feet, projecting 9 inches 
all around. The piers were lengthened at the belt-course by 
adding semicircular ends from that point to below low-water. 
Main wall under belt-course 37.42 X 11.72 feet, bottom of neat 
work 42.20 X 16.50 feet, height 59.39 feet. Then four offset 
courses 8.58 feet thick, bottom dimensions 49.00 X 23.00 feet. 
Total height 97.32 feet. Piers 4 and 5, carrying channel span 
420feet,top 26.25X 10.55 f eet > at topof belt-course 28.88X 13.20 
feet. Main wall under belt course 42.24 X 1336 feet. Bottom 
neat work 46.92 X 18.04 ^ eet - Three offset courses 5.6 feet 
high. Bottom dimensions 51.72 X 22.84 f eet - Total height 
96.86 feet for No. 4 and 101.60 feet for No. 5. Square ends 
to belt-course, rounded ends to bottom. Pier No. 6, carrying 
200-feet span, top 22.00x6.00 feet, bottom of neat work 27X11 
feet, height of shaft 59.88 feet. Two offset courses 5 feet 
thick, bottom dimensions 31.06 X 14.60 feet. Total height 
64.88 feet. This case is entered into as well illustrating a 
good standard of dimensions and form of piers. Minimum 
dimensions for piers carrying length of spans above called for. 
All of these piers had raising stones of Berea, Ohio, sandstone, 
a hard, strong stone. The coping was doubled, the bottom 
course projecting 9 inches all around. Thickness of each 
course was 18 inches. A cone-shaped finish was placed at the 
ends on top of the belt-course in passing from the curved ends 
to the square ends. The pedestals were 4 feet square under 
coping, coping 1 5 inches thick, projecting 3 inches. Top of ped- 
estal was from 2 to 4 feet above ground. Two offset courses 
below ground, generally built of only two stones to the course, 
sometimes three stones allowed in the footing-courses. It is 
best to arrange elevation of the top of the coping, where the 
ground will allow, so as to have as many trestle-bents of the 
same height as possible. 

For elevation and plan of pier as just described, see Plate 
I, Figs. 1 and 2. 



136 A PRACTICAL TREATISE ON FOUNDATIONS. 

Article XXVIII. 

DEFINITIONS. 

PARTS OF THE ARCH. 

289. Abutment. — The masonry supports of the arch ring. 

Skew-back. — A course of stone on top of the abutment, 
with an inclined surface from which the arch directly springs. 

Arch Ring. — The masonry of the arch between the intrados 
and extrados. 

Intrados or Soffit. — The under curved surface of the arch 
ring. 

Extrados or Back. — The top curved surface of the arch 
ring. 

Crown. — The highest part of the arch. 

Springing Line. — The line on the soffit at the top of the 
abutment. 

Haunches. — The lower part of the arch ring on both sides. 

Spandrels. — A wall, or walls, built on the top of the arch, 
commonly one at each end and in the plane of the face, 2 to 5 
feet high. 

Span. — The horizontal distance between springing lines. 

Rise. — The vertical distance from the springing to intrados 
at the crown. 

Ring-stones. — A course of stones between two vertical 
planes ; does not actually exist, as the stones break joints, 
there being no continuous joint in a plane parallel to the face 
of the arch. The face stones, or those seen on the ends of the 
arch, are frequently cut on top with a horizontal and vertical 
surface which project above the extrados. 

String-course. — A course of stone extending from end to 
end of the arch. 

Strifig-course Joint. — The joints between the string-courses, 
continuous and in the same plane from end to end of arch. 

Semicircular or Full Centre Arch. — One in which the in- 
trados is a full half of the surface of a cylinder. 



DEFINITIONS. 1 37 

Segmental Arch— One in which the intrados is less than 
the surface of a semi-cylinder. 

Elliptical Arch. — One in which the intrados is part of an 
elliptic cylinder ; one in which the rise is less than the half-span. 

Pointed Arch. — One in which the rise is greater than the 
half-span, generally formed by the intersection of two equal 
circles. 



DEFINITION OF PARTS OF PIERS, RETAINING-WALLS, ETC., 

290. Face. — The exposed part of a pier or wall. 
Facing Stone. — The stones that show on the face of the 
wall. 

Backing. — The stones behind the facing stones in retaining- 
-walls and between the face walls in piers, and well bonded to 
the face stones. Also called filling, whether of large stones, 
rubble, or concrete. 

Batter.— The inclination of the face of a wall to a vertical, 
generally expressed in fractions of the height, as £ inch, 1 inch,' 
1 J inch to 1 foot vertical; ordinarily £ inch to 1 foot. 

Bond.— The overlapping of the stones so as to tie the wall 
together. 

Course.— A layer of stone between two horizontal planes or 
joints. 

Joints.— The space between the stones, generally filled with 
mortar. The bed-joints are the top and the bottom, generally 
horizontal; and the side-joints, which are either vertical or 
inclined, generally vertical. 

Stretcher.— A stone that shows its full length on the face 
and all stones parallel to it in the backing. 

Header. — A stone that shows its end on the face and all 
parallel to it in the backing. 

String or Belt Course.— A course of large stones, projecting 
from 6 to 9 inches from the face of the wall ; generally dressed 
smooth on the exposed part, and also has a wash cut on it. 
Used mainly for appearances, and marks a change from a 
curved to a plain finish to a pier. 



I38 A PRACTICAL TREATISE ON FOUNDATIONS. 

Coping.— A course of large stones on the top of the pier r 
projecting from 6 to 9 inches, dressed true on all surfaces ; 
has a wash on the projecting part. Sometimes two coping- 
courses are used. The upper one has no projection, and in 
fact the lower coping projects beyond the upper 6 to 9 inches. 
These coping-stones are commonly bolted to the pier, or 
fastened to each other by cramps or dowels. 

Pedestal or Raising Stones. — Large thick stones of some 
hard variety, placed on top of coping, upon which the ends of 
the bridge directly rest. These are not always used. 

Pointing. — Cleaning out the joints to the depth of 1 to 1^- 
inches, and refilling with good mortar. 

Quoins or Corner-stones are stones at the corner showing 
header on one face and stretcher on the other. 

Dozvcls. — A straight bar of stone or iron, fitting into holes 
cut in the sides or beds of adjacent stones so as to prevent one 
lifting without the other. 

Cramps. — Iron bars 18 to 20 inches long, bent at right 
angles at the end for 2 to 3 inches and placed across the joint, 
the bent ends let into holes cut in the top of the stone ; a 
groove also being cut between the holes so that the bar will 
not project above the surface of the stone. Hot lead, sulphur, 
or cement, is generally poured around the bar to fasten it in 
place. 

291. The character of the masonry is determined by the 
size of the stone, the regularity of the courses, the amount of 
dressing or cutting. 

Ashlar Masonry or Block-in-course. — Masonry laid in regular 
courses with bed-joints horizontal and side joints vertical ; 
all the stones cut into regular blocks; all surfaces dressed 
smooth except the face. This may or may not be dressed. 

Random or Coursed Rubble. — Masonry in which the stones 
are cut to regular shapes, side joints vertical, bed-joints hor- 
izontal but not continuous, courses of varying thicknesses, 
stones being large and small, thick and thin. 

Common Rubble. — Masonry in which the stones are built as 



DEFINITIONS. 1 39 

they come from the quarry, with no regular courses ; the joints 
are not necessarily either vertical or horizontal. Large and small 
stones are used at random and with or without mortar. 

Stones. — The upper and lower surfaces are called beds, the 
remaining parts are called sides, face, and back. 

Quarry-faced. — When the face is left as it comes from the 
quarry. 

Rock-faced. — When the face is roughly hammered so as 
not to project more than from 3 to 5 inches. 

Pitch Line. — When a straight, well-defined line at the 
angles is cut all around the face of the stone. 

Chisel Draft. — When a smooth, plane surface from 1 to 
\\ inch is cut around the face of the stone, forming well- 
defined and regular angles ; the rest of the face left rough. 

292. The face of the stones may be left rough. If the face 
has no projection over \ to £ inch, it is said to be rough- 
pointed ; if the projections are not over T ^ to \ inch, it is 
called fine-pointed, and is what is generally understood by 
dressed stone, whether for face or for beds ; on the face it is 
made to look uniform and regular. When required to be of a 
smoother surface than the fine-pointed, it is generally said to 
be bush-hammered ; this is, however, done by an instrument 
called the crandall, which consists of a number of double- 
pointed steel pins fastened close together in a slot at the end 
of an iron bar, and produce a smooth and more regular surface 
than the fine point. The bush-hammer is not commonly used 
by stonecutters. The crandall or bush-hammer is only required 
for dressing coping or cutwater stones. For perfectly smooth 
faces the stone is first sawed and then rubbed to a smooth 
surface. It is only used for ornamental purposes. 

293. The common way of raising large heavy stones to 
their position on the wall is by means of derricks, which con- 
sist essentially of a mast of greater or less height, resting on a 
solid block of wood and a boom connected with it at or near 
the bottom, and also by a rope at the top. A hoisting rope 
passes from a drum or capstan over a sheave in the top of 



140 



A PRACTICAL TREATISE ON FOUNDATIONS. 



the boom and thence downward, terminating in a chain which 
has hard steel hooks at the bottom. Holes, for the hooks, 
are cut into the sides of the stone a little above the line passing 
through its centre of gravity. This is the common mode. 
Sometimes a dovetailed mortise is cut into the top of the stone, 
thicker at the bottom than at the surface, and a lewis made of 
three pieces of iron, two of which are truncated wedges, the 
other rectangular. The wedge-shaped pieces are first inserted, 
and are forced apart by driving the straight piece between 
them. The hoisting chains are attached to the wedge-shaped 
pieces, which can not be pulled out without breaking the stone. 
This, however, is only applicable to hard, strong stone, unless 
the mortise is cut very deep. Another method is to drill two 
holes, in a plane passing through the centre of gravity of the 
stone, inclining towards each other at an angle of 90 , or 45 
to the vertical on either side ; strong iron bars are inserted in 
these holes, and chains are fastened to eyes on the other ends 
of the iron bars. 

For details of common forms of derricks, see Plate V, Figs. 
5, 6, and 7 ; and forms of derrick set on top of pier and lifted 
by screws as the masonry is built, see Plate V A, Fig. 1. 



Tables or Ultimate Strength of Stones, Natural and Artificial, 

to resist Crushing, Tearing, or Cross-breaking, as given by 

Several Authorities, in lbs. per Square Inch. 



294. 



TABLE 1. 



Resistance to Crushing, 
in lbs. per square inch. 



Granite 

Marble 

Limestone 

Sandstone 

Slate 

Brick 

Brick-work 

Brick-work in cement.. 



Rankine. 



I2,S6l 



S.52S to 3,050 
9,824 to 3,000 



1,100 



Soo to 1,000 



Baker. 



12,000 to 21,000 
S.ooo to 20,000 
7,000 to 20,000 
5,000 to 15,000 



2,500 to 3,000 
1,150 to 1,290 
1,650 to 1,850 



Trautwine. 



6,222 to 

4,000 to 

4,000 to 

2,333 to 

6,222 to 

800 to 

310 to 

465 to 



12.444 
9.340 
9.340 
6,999 

12,444 
4, 800 

465 
1,162 



DEFINITIONS. 
TABLE 2. 



141 



Transverse Strength or 
Resistance to Cross-break- 
ing, in lbs. per square inch 
Modulus of Rupture. 



Granite 

Marble 

Limestone and / 

Sandstone ) 

Slate 

Brick 

Brick-work, common. 
Brick-work in cement. 



Rankine. 



Baker. 



900 to 2,700 
144 to 2,800 

576 to 2,340 

1,800 to 9,000 
269 to 1,796 



200 to 380 



Trautwine.* 



900 to 2,700 



360 to 1,260 

3,600 to 5,700 
180 to 540 



295. Although there are considerable differences between the 
resistance to crushing of the stones above given, no inconven- 
ience or doubt need rise as to the strength of any of the above, 
as 200 lbs. per square inch is an unusual pressure, and this only 
exists under the largest and highest structures, and then only 
when the normal unit pressure is increased by wind pressure 
on the leeward side. 

296. To apply the table of crushing strength to any struc- 
ture, it is only necessary to multiply the unit pressure in the 
column by the area of the cross-section in the same unit to 
obtain the total resistance to crushing, as R = pA, in which/ 
is the unit or coefficient of resistance to crushing in lbs. per 
square inch or per square foot, and A is the number of square 
inches or square feet in the base of the structure, and R the 
total resistance to crushing. For example, take the average 
area of a pier built of sandstone to be 22 X 40 = 880 square 
feet. In the column from Rankine's Engineering the least 
resistance of sandstone to crushing is 3000 lbs. per square inch 
= 432,000 lbs. per square foot, or 216 tons of 2000 lbs. 
per square foot, hence R = pA — 216 X 880 = 190,080 tons. 
Now to determine the height of a sandstone pier that 
would crush at the base under its own weight (assuming that 
it does not give way by flexure or transverse strain, the limit 

* Trautwine always takes the lengths of beams (/) in feet, in which case the 
moduli of rupture are only ^ s of the numbers in this table. See Trautwine, 
page 185. 



142 A PRACTICAL TREATISE ON FOUNDATIONS. 

of which is generally taken at a height not over 20 times its 
least dimension, a height which rarely occurs in practice. (The 
height of the Washington Monument is 500 feet to the bottom 
of the pyramidal finish, and the least diameter of the column 
36^ at top, and 50 ft. at bottom ; the middle would be 43^ ; 
therefore the height is only 14 times its least diameter.) The 
ultimate crushing strength is 216 tons per square foot, or 
432,000 lbs. ; assuming that the weight of sandstone masonry 
is 140 lbs. per cubic foot, we have 140 X y = 432,000, hence 
the required height y — 3685 ; and in the same manner the 
height of a brick column, assuming brick to weigh 12$ lbs. per 
cubic foot, would vary from 600 to 900 ft. to crush of its own 
weight, and a granite pier about 8000 ft. high. In selecting 
the unit of resistance to crushing from the tables, whether you 
take the least or the average or the greatest, depends upon 
the kind or quality of the stone considered. (Table 1.) 

297. The base of a brick chimney at Glasgow, Scotland, 
468 feet high, bears 9 tons per square foot, and in high winds 
may have to bear as much as 15 tons per square foot, or 210 
lbs. per square inch at base ; and Mr. Trautwine expresses the 
opinion that first-rate hard brick laid in cement would carry 
without completely cracking 100 tons per square foot or 1400 
lbs. per square inch. « 

298. So far as stone is concerned, the main application of 
the table of transverse strength is in the case of lintels over 
openings, which in general are to be considered as beams uni- 
formly loaded ; but as they may sometimes also be subjected 
to a single concentrated load at the centre, it will be well to 
apply the formula for both cases, although the first is two times 
as great as the second. The writer will use Rankine's formula, 
which is easy to remember, when the principle of moments 
is understood, is easy of application, and applies to all condi- 
tions of loading and supporting beams, which will be further 
explained in connection with timber. The formula is: mWl = 
•ufbli 1 , in which ;// is a factor depending upon the manner of 
loading and supporting the beam, Wis the concentrated weight 
at the middle point between the supports ; / is the length of 



DEFINITIONS. H3 

the beam or clear span in inches ; n is a factor depending on 
the cross-section of the beam, and for rectangular beams is 
equal to \\ /is the modulus of rupture in lbs. taken from the 
table ; b is the breadth in inches, and h is the depth in inches. 
Suppose a lintel to be 10 inches thick, 2 feet wide, and 10 feet 
long, loaded with a single weight at the centre, the lintel to 
be rectangular in cross-section, and the stone granite ; then 
m = i, 1= 1 20 inches, n = \,f— 2700, as this would always 
be the best and strongest stone ; b = 24 inches, and h = 10 
inches. Substituting in the formula, we have 

4 X 2700 X 2 4 X 100 
IWX 120 = * 2700X24 X 100; W= 6x I20 > 

hence W = 36,000 lbs. centre-breaking load. When uniformly 
distributed over the beam, it would be double the above, or 
72,000 lbs., as will be seen from the formula ; W, in this case, 
= wl, in which w = weight on a unit of length, and m = •§-, all 
other values of same ; hence 

8 X 2700 X 24 X 100 
*(«")' = * 2700X24X100; or, wl= 6x I20 > 

hence W—wl— 72,000 lbs. For other materials and other 
dimensions similar results can be obtained, using Table 2 for 
transverse strength. 

299. In practice, under steady loads, it would not be safe 
to rely upon more than from \ to \ of the above loads ; but it 
is safer to use only from \ to T V of the above results; that is, 
for a granite beam of the dimensions given above, it should 
not be loaded with more than 7200 lbs., or 720 lbs. per foot of 
length. 

300. TABLE 3. 

Table of Tensile Strength of Mortar in Pounds per Square Inch. 

(From Baker.) 
Hydraulic, with sand, 30 to 300, age from 1 week to 1 year, 1 sand, 1 cement. 
Hydraulic, j neat ) from 40 to 400. 

Cement, \ cement S from ioo to 800, age from 1 day to 1 year. 
Cement' and sand, from 80 to 350, age from 1 week to 1 year, 3 sand, 1 cement. 



144 A PRACTICAL TREATISE ON FOUNDATIONS. 

301. The adhesive strength of mortar varies greatly with 
the kind of cement used and the proportion of sand, the clean- 
ness of the surface of the brick or stone, whether porous or not. 
Mr. Rankine gives 15 lbs. per square inch to limestone and 33 
lbs. per square inch to brick. According to Baker, in Portland 
neat cement the adhesive strength varies for limestone from 57 
to 7S lbs. per sq. in. and from 19 to 213 lbs. per square inch 
for brick; and when mixed, I cement, 2 sand, the adhesive 
strength varies from 5 to 140 lbs. per square inch, according to 
the character of cementing material and stone used. 

302. The absorptive power may be taken as one part for 
from 80 to 700 parts in granite, and 1 part in from 30 to 60 of 
sandstone, limestone from 1 part in 20 to 1 part in 500, and 
for brick from I part in 4 to I part in 50, and mortars from I 
part in 2 to 1 part in 10. In general a small absorptive power 
is an indication of a good quality of stone. 

303. According to Rankine, the expansion of stone is as 
follows: brick, .00355 of its dimensions; sandstone, .0009 to 
.0012; marble, .00065 to .0011 ; granite, .0008 to .0009 of their 
linear dimensions in a range of 180 Fahr. 

304. TABLE 4. 

Table of Weight in Pounds per Cubic Foot of many Substances. 

(From Trautwink.) 



Granite 16S 

Limestone I7 2 

Marble 172 

Sandstone 150 

Slate 175 

Common brick 125 

Pressed brick 150 

Masonry of — 

Granite 165 

Rubble 125 

Sandstone 144 

Common brick 125 

Pressed brick 140 



Sand 99 to 117 

Sand, packed 101 to 119 

Sand, wet 120 to 140 

Clay, dry 63 

Ordinary earth 72 to 92 

Ordinary earth, packed. ... 90 to 100 

Mud. 104 to 120 

Hydraulic cement 60 to So 

Portland cement 80 to 87 

Mortar, dry 100 

Concrete ... 

Water 62.33 



DEFINITIONS. \ 4$ 

The above table is useful in determining the stability of 
retaining-walls, weight of structures, and force tending to over- 
turn the wall or to cause sliding. 

305. The following are the angles of repose or the angles 
of friction between different substances heretofore considered : 



TABLE 5. 

(From Tkautwine.) 

Coefficient 
of Friction. 

Polished marble on polished marble 9 6' 0.16 

Polished marble on common brick 23 45' 0.44 

Common brick on common brick 32 38' 0.64 

Common brick on dressed soft limestone 33" 2' 0.65 

Common brick on dressed hard limestone 31" 00' 0.60 

Hard limestone on dressed hard limestone 20 48' 0.38. 

Hard limestone on dressed soft limestone 33" 50' 0.677 

Soft limestone on dressed hard limestone 33 2' 0.65. 

Masonry and brick-work, dry 33 2' 0.65 

Masonry and brick-work mortar, damp 36'' 30' 0.74 

Masonry and brick-work, dry clay 27" 00' 0.51 

Masonry and brick-work, moist 18 15' 0.33 

Wet clay 14" to 17" 0.25 to 0.31 

Dry clay 2 1" to 37" 0.38 to 0.76 

Damp clay 45° oc/ 1.00 

Shingle and gravel 35 to 48 0.70 to 0.90 

This table is useful in determining stability of walls and 
arches against sliding in connection with weight of walls and 
position of plane of rupture in calculating the thrust exerted 
against walls. To determine resistance to sliding of one body 
on another multiply normal component of weight of one body 
resting on another by the coefficient of friction, if the surfaces 
are inclined, and the entire weight if the surfaces arc horizon- 
tal. What is the resistance of a block of dry masonry weighing 
20 to sliding on any ioint? 20 X .65 = 13 tons. 



146 A PRACTICAL TREATISE ON FOUNDATIONS. 



306. 



TABLE 6. 



The Bearing Power of Soils in Pounds per Square Inch and Tons 
per Square Foot. 



Clay, dry 

Sand 

Clay and sand 

Sand and gravel 

Clay, wet 

Layer of clay over quicksand 
Alluvial soil. New Orleans.. 



Rankine, Safe Load. 



Lbs. per 

sq. in. 



17 to 23 



Tons per 
sq. ft. 



Ii to If 



Baker, Safe Load. 



Lbs. per 
sq. in. 



Tons per 
sq. ft. 



55 to 


86 


55 to 


86 


55 to 


86 


in to 


140 


20 to 


30 


20 to 


40 


7 to 


14 



4 to 8 
4 to 6 
4 to 6 
8 to 10 
1\ to 2 

litO 2| 
I tO I 



Ulti- 
mate 
Load, 
tons 
per 
sq. ft. 



15 

15 



We may then safely conclude that ordinary soils can be 
easily loaded with from 2 to 3 tons per square foot or from 
4000 to 6000 lbs., and for softer soils, or firm soils resting on 
softer soils, 2000 to 4000 lbs. per square foot. 



PART SECOND. 



Article XXIX. 

TIMBER FOUNDATIONS. 

UNDER this heading are included simple timber foundations; 
piles, whether cut off under ground or under water, as well as 
when left standing above the surface, as is the case in pile 
trestles; framed trestles ; timber piers for bridges ; timber cribs, 
whether filled with concrete or broken stone ; open timber 
■caissons; coffer-dams; Cushing cylinder piers; etc. 

TIMBER. 

I. Timber is used extensively in the above structures for 
the following reasons : 1st. As a matter of economy. It is often 
impossible to procure stone or brick in any reasonable time or 
cost, but timber of some kind can commonly be procured 
which will at least do for a structure of a temporary character ; 
and if under water or in wet or even constantly moist ground, 
it can be relied upon for the foundations of permanent struct- 
ures, as it will not rot when constantly wet. When immersed in 
sea-water it is rapidly honeycombed and destroyed by sea-worms, 
unless creosoted. 2d. Timber which, either on account of its 
small dimensions or excess of sap, would be unsuitable for 
structures above ground, may be suitable for those underwater 
or under ground. 3d. Timber is easily framed and handled, 
and can be transported overland or floated in large rafts on 

147 



I48 A PRACTICAL TREATISE ON FOUNDATIONS. 

rivers or streams, yet has the strength to bear heavy loads, 
and strains. But be sure that the timber will always remain 
wet. 

2. Under walls of houses pieces of plank, 5 to 6 feet long 
and from 2^ in. to 3 in. thick, can be placed side by side 
on soft materials, thereby securing increased bearing sur- 
face, and by using from two to four courses placed at right 
angles to each other the base can be spread to a width of 
10 to 12 feet, allowing structures of considerable weight to be 
built on very soft foundation-beds, such as silt or quicksand. 
Sometimes a series of rough logs are laid longitudinally, either 
side by side or at short intervals, the intervening space filled 
with sand, broken stone, or concrete, and one or more courses 
of plank placed over and at right angles to these ; or two or 
more courses of logs crossing each other, the intervening spaces, 
if any, filled as stated above. This last constituted the founda- 
tion of the New Orleans Custom-house, a large, heavy, and mass- 
ive granite building; it is true that in this some settlement has 
taken place, but no serious damage has resulted. By either of 
the above methods many houses, culverts, and other structures 
are safely and economically constructed. In such cases the 
probability is that whatever settlement takes place will be uni- 
form under the entire structure, and no damage to the structure 
will follow unless high and heavy towers or steeples are bonded 
into the structure ; in such cases the spread of the base should 
be such as to insure that the unit pressure shall be the same as 
under any other portion of the structure. Piles are better under 
such very heavy loads, and should always be used if there is 
any possibility of the material being washed or scoured out. 

3. Under large and heavy piers for bridges it is not unusual 
to build cribs made of round logs or square timber, crossing 
each other and bolted together at each intersection, leaving 
cells or pockets to be filled with broken stone or concrete ; in 
such cases the crib is really intended to confine the filling ma- 
terial, but of course supporting its proportionate share of the 
load. If the filling is gravel or broken stone, iron rods should 
be used to tie the sides of the crib together so as to prevent 



TIMBER FOUNDATIONS. 149 

•any tendency to bulging; this is not necessary when concrete is 
used. The dimensions of such cribs should be from 4 to 6 feet 
greater all around than the masonry structures resting upon 
them. If the crib has to be sunk through any depth of water, a 
plank bottom will have to be used over the entire bottom, or at 
any rate under a sufficient number of the pockets to hold the 
weight necessary to overcome the buoyancy of the water. It is 
not advisable to endeavor to sink the cribs by building the 
masonry, as the cribs will rarely rest on the bottom in a per- 
fectly level position. With broken stone or concrete filling this 
is a matter of little consequence, unless very much inclined, 
as it can be easily levelled with broken stone or concrete, and 
the masonry commenced by the use of a cofferdam if neces- 
sary, but usually the crib is built to within 2 or 4 feet of the 
surface of the water. The bed of the stream is generally 
levelled by dredging; this serves also to remove the soft 
and loose material at the bottom, but it generally requires 
removing the material over a large surface, if it is desir- 
able to reach any great depth below the bed of the river, 
adding materially to the cost ; and unless stiff clay is close to 
the bottom the obstruction to the current will almost always 
cause a scouring action, endangering the safety of the structure. 
It can hardly be recommended as a safe and satisfactory foun- 
dation. (See Plate IV, Elevations, Figs. 5 and 6.) 

4. Many examples, however, exist, and have stood the test 
of time. The Parkersburg (W. Va.) bridge across the Ohio 
River was thus constructed ; the piers of this bridge stand 90 
feet above water, and rest on a bed of gravel and sand at a 
depth of 12 ft. below the bed of the river; the excavated pit 
was 100 by 50 ft. ; the crib or grillage was composed of three 
courses of timber 12 in. by 12 in., bolted together, 78 ft. long 
by 28 ft. wide; this carried a pier 120 ft. high, with spans of 
350 ft. Giving a pressure of 9080 lbs. or 4^ tons (about) to the 
square foot on gravel and sand. A rod was driven 25 ft. into this 
material. An open caisson was built, the grillage forming the 
bottom, this was sunk on the gravel bed by the weight of the 
masonry itself, and was practically level when it rested on the 



ISO A PRACTICAL TREATISE ON FOUNDATIONS. 

gravel. These piers were finished 15 ft. wide on top ; 10 ft., 
would have been ample. 

5. If a crib is to be sunk on a bed of rock which is very 
irregular or much inclined, two methods of procedure are 
open : 

1st. To blast the rock to a level or nearly level surface ; this 
is difficult, slow, and expensive. 

2d. If the rock is irregular, with elevations and depressions, 
or not having any great and uniform inclination, the crib can be 
sunk until it almost reaches the higher point or points, and. 
while suspended in this position broken stone can be dropped 
into the pockets and around the outside, the stone assuming its 
own slope below the crib, and this continued until the crib is 
found to be uniformly and solidly supported ; the masonry can 
then be commenced. Cement can be forced through pipes be- 
tween the broken stone, thereby forming a solid and compact 
mass. (See Plate VIII, Elevations, Figs. 5 and 6.) 

COFFER-DAMS. 

6. If the material composing the bed of the river is gravely 
sand, clay, or silt, and either too soft to build upon, or is at 
all likely to be scoured out, instead of the preceding methods, 
the space to be occupied by the structure must be sur- 
rounded by a water-tight dam of some kind, so that the 
water can be pumped out of the enclosed space, and the 
excavation and preparation of the foundation-bed proceeded 
with as on dry land. The structure for this purpose, of 
whatever material it may be constructed, is called a coffer- 
dam. If there is no material depth of water, not exceed- 
ing 5 ft., and no current, clay either alone or mixed with 
sand and gravel can be dumped in the water, so as to form an 
earthen dam entirely around the space to be enclosed, and 
carried up 2 or 3 feet above the water surface, finished at 
least 3 ft. wide on top, the earth assuming its own slope below 
the water surface ; this slope will be rather flat, from two to- 
three horizontal to one vertical. The material to be excavated,, 



TIMBER FOUNDATIONS. 151 

being saturated with water would, also require a long flat 
slope, consequently the area enclosed should be large in com- 
parison with the area of the base of the structure ; for instance, 
if the base of the structure is to be 20 ft. wide and the depth 
excavated is 15 ft. below the water surface, the interior width 
of the dam should not be less than from 80 to 1 10 ft., and the 
length generally from two to three times the width. Owing to 
the great dimensions required, this kind of dam is rarely used, 
and resort is had to the ordinary timber-coffer dam, constructed 
as follows: 



Article XXX. 

COFFER-DAMS OF TIMBER. 

7. Two rows of guide-piles, the piles of the proper length 
and at least 12 inches in diameter at the larger end, are driven 
entirely around the space to be enclosed. The area of this space 
should be considerably greater than the largest area of the 
structure to be built. If the dimensions of the base of the 
structure are 20 X 43 feet, the inside dimensions of the dam 
should under no circumstances be less than 6 feet more than 
the above, or 26 X 49 feet, and in general should be governed 
by the depth to be excavated below the bed of the river, the 
increase being at least equal to the depth, and better if equal 
to \\ times the depth; or for a depth of 10 feet below the bed 
of the river the dimension in the above case should not be 
less than 30 X 53 feet, and economy will justify an increase to 
35 X 58 feet. More failures in coffer-dams result from the 
fact that the enclosed area is made too small, than from any 
other cause. A false idea of economy in the beginning gen- 
erally results in much loss of time and a largely increased 
expenditure in the end. The dimension of the dams having 
been settled, the two rows of piles are driven so that the 
piles in each row will be from 4 to 8 feet apart, and the rows to 
be from 5 to 8 feet apart, according to the height of the dam 
above the bed of the river. This clear distance between rows 



152 A PRACTICAL TREATISE ON FOUNDATIONS. 

will allow from 3^ to 6£ feet in thickness of the clay puddle. 
This width is required to give stability to the dam. From 18 
inches to 2 feet of good clay puddle is ample to prevent leaks. 
Wale-pieces, that is, horizontal pieces of timber, generally 6 X 
12 inches, and of varying lengths, are bolted to the rows 
of piles, facing each other between the rows. Bolts, 1 inch 
diameter and from 7 to 9 feet long, tie the rows together. 
These are placed above the Avater surface. Another set of 
wales should now be placed, resting against the piles at or near 
the bed of the river. This is done by fastening battens to a 
wale-piece of any length, and forcing the wale-piece to the bed 
of the river, the battens then spiked at their upper ends to the 
top wale-pieces. This is carried all around both rows of piles, 
leaving spaces or gaps between the ends of the wales. Then 
other pieces are lowered in the same way, resting on top of the 
first pieces, and covering the vacant spaces between them. Inter- 
mediate rows of wales should be placed as above described, so 
that the vertical distance between any two sets of wales should 
not exceed 6 feet. Sheet-piles (planks of about 2|- to 3 inches 
thick, and of lengths depending upon the depth of the water) 
are now driven, either by a heavy mall or a light hammer 
guided by leads as in pile-drivers, close together and resting 
against the wales. These should penetrate from 18 inches to 
5 or 6 feet into the bed of the river, depending upon the ma- 
terial in the bed of the river. These sheet-piles are sharpened 
at the lower end, so that the bevel extends the entire width of 
the plank, i.e. from 7 to 12 inches, and when driven this bevel 
tends to hold each plank up against the last one driven. This 
forms a double close sheeting entirely around the enclosed 
space. Each plank when driven is spiked to the upper wale- 
piece. This then leaves a space to be filled with the puddle, 
varying from 3^- to 6^ feet in width. The guide-piles should be 
driven well into the bed of the river, and if practicable should 
pass through any sand or gravel into clay ; but if the dam is 
made large enough, a penetration of from 10 to 15 inches into 
the bed, of whatever material that may be found, will in gen- 
eral be sufficient. The puddle can now be thrown in between 



TIMBER FOUNDATIONS. I 53 

the sheeting, and should be rammed or rather cut with a ram- 
mer head of 3-inch plank trimmed to a wedge-shaped edge. 
This prevents the formation of distinct layers. Each is cut 
into the layer below, binding the entire mass, and has a similar 
effect to the ribbed roller used in making reservoir embank- 
ments. The dam is now ready to be pumped out. Many 
authorities say that the soft and loose material between the 
sheeting should be dredged out. The writer does not compre- 
hend the meaning of this. It is not necessary if the bed of the 
river is clay, nor is it necessary in gravel and sand, this being 
considered by many as the best material with which to puddle. 
If alluvial soil or silt, this is good puddle itself, and is not only 
water-tight, but often air-tight. It can hardly be necessary 
to do any dredging, unless limbs of trees or brush should be 
encountered. These would conduct water through the dam, 
and might cause dangerous leaks. The writer at least never 
did any dredging for this purpose, and has had good success 
in the many dams constructed by him. The construction of 
other forms of dams will be described before entering into a 
description of pumping and excavating, as these 'process will be 
the same for all. (Figs. 3 and 4, Plate IV.) 

8. Sometimes four rows of wales are used, these being 
placed both on the outside and inside of the rows of piles, and 
the sheet-piles are driven between the wale-pieces. This 
guides the sheet-piles to some extent while being driven, but 
has no other advantage ; requires more timber, is good 
practice, though not necessary. Sometimes the sheeting, in- 
stead of being 3 inches thick, is as much as 8 or 10 inches 
thick, with a tongue cut on one face about 2 to 2\ inches 
broad and about the same depth, and a similar groove cut on 
the opposite face, and then driven so that the tongue of one 
piece fits into the groove of the adjacent piece. This certainly 
causes much expense in framing, and also delay in driving, and 
great waste of timber. This can never be necessary if a 
double wall is used, but will make a good single-wall dam, but 
will require strong bracing on the inside. There is probably 
no economy in this plan. Sometimes a groove is cut on both 



154 A PRACTICAL TREATISE ON FOUNDATIONS. 

faces. The sheet-piles are then driven as close together as 
possible, -and a 2-inch plank is driven in the grooves. This 
will close any opening that may exist by the piles leaning from 
each other in driving, and is to be preferred to the first or 
tongue-and-grooved method ; or strips are spiked to the face of 
the piles, one strip on one face forming a tongue, and two 
strips on the other forming a groove, and driven as described. 
This prevents waste of timber, but is not as good as either of 
the other plans, unless the timber is very soft or splits easily, 
in which case the strips spiked on will be stronger than the 
regular tongue and groove. The writer thinks that the ordi- 
nary puddle-dam will prove more economical, more expedi- 
tious, and more satisfactory than either of the three last-men- 
tioned methods. (See Figs. 3A and 4A, Plate IV.) 

9. A solid wall of timber, either made of 12 X 12 in. sticks 
or plank, laid horizontally on top of each other and spiked or 
bolted together, which can be framed floating on the water, 
and large enough to enclose the required area, can be built 
and sunk into a dredged hole, or resting on the natural bed of 
the river, and sheet-piles driven all around and close against 
the timber wall to which they are spiked or bolted, will make 
a good dam, but will have to be strongly braced on the interior. 
This dam, when built in a circular or octagonal form, as is 
required in case of pivot piers for drawbridges, has many ad- 
vantages, is easily and rapidly constructed, contains a minimum 
quantity of timber, will require little or no bracing on the 
interior, and, even if requiring large guide-piles to be driven 
on the inside to stiffen and hold it steady, will prove economi- 
cal. This will make a good dam, when the bed of the river is 
a rocky ledge, by sinking it on the rock and throwing clay 
puddle all around on the outside, unless the current is so rapid 
as to Avash away the puddle. In this case a double wall built 
as above described, and connected by cross-pieces of timbers 
for strut and tie braces, dovetailed or bolted to the walls, 
and the space between the walls filled with puddle, will make a 
stronger dam than any other described ; can be rectangular, oc- 
tagonal, or circular in plan ; of any size or height required ; will 



TIMBER FOUNDATIONS. I$S 

need little or no interior bracing. Sheet-piles should be driven 
in earth bottoms as deep as practicable, and on rock should be 
driven so as to broom or batter the lower ends, so that they 
may conform to the irregularities of the bottom; this will hold 
the puddle, and to a large extent prevent leaks along the rock 
under the puddle. Where the rock has a regular inclination 
or slope this crib-dam can be easily built so as to conform to 
the slope of the bottom. It should always be used in 
case of a rocky bottom. It is called the crib coffer-dam. In 
very rapid currents it can be built in sections of short lengths 
shaped as truncated wedges, alternate sections held and sunk 
in place and heavily weighted, the closing sections then floated 
and forced into their places by the force of the current, and 
then arrangements for holding the puddle can be made by 
uprights and sheeting in the enclosed space. This method 
can be used where the above-described method scould not be 
used. (See Figs. 5 and 6, Plate IV.) 

10. Mr. J. E. Robinson has a patent dam which has some 
merits worthy of notice, which does not, however, seem capa- 
ble of economical application, except in shallow water and 
where no great current exists. It is to be always circular 
in form, regardless of the shape of the pier. It is constructed 
as follows : A series of shears or three pieces of timber held 
together by bolts passing loosely through the pieces at the top, 
allowing the legs to be spread out at any angle with each 
other; these are set up at intervals on the circumference of a 
circle ; each has a small block and tackle fastened to its apex ; 
large sheets of iron plate are then suspended under the shears. 
These plates are bolted together, forming a circular sheeting; 
inside of this long timbers, 12 in. X 12 in., slightly bevelled, as 
in arch stones, are driven with a light hammer, close together 
and resting against the iron sheeting. The space thus enclosed 
is ready then to be pumped out. This certainly forms a strong 
dam, even without interior bracing, when properly constructed,. 
but in considerable depths radial bracing will be found neces- 
sary to prevent the bottom of the timbers from pressing in- 
wards. The objections or defects arise mainly from driving 



156 A PRACTICAL TREATISE ON FOUNDATIONS. 

the piles, as it is difficult to keep them in contact for their full 
length, and they will almost always separate or spread at their 
lower ends ; this can, at least in part, be overcome by cutting 
grooves in the piles and driving filling pieces of iron or wood 
in the grooves, as previously described. Owing to the form of 
the dam, the excavation is confined to a narrow area in the 
direction of the length of the pier, coming close to the sides of 
the dam along one diameter, and leaving broad, unexcavated 
spaces on either side. In addition, the excavated material is 
for convenience thrown on top of the undisturbed earth ; the 
tendency of this is to bulge the sides out, and the great excess 
of outside pressure, in a direction at right angles to this, tends 
to force this part of the dam in, and aids in forcing the other 
parts outwards This distorts the entire dam ; a portion of the 
dam comes in and another portion goes out, causing leaks that 
are hard to be controlled. In the writer's experience these 
dams gave great trouble and caused much delay ; but in one 
case, at the Schuylkill River, this was used where an ordinary 
coffer-dam had failed entirely, and under circumstances pecu- 
liarly trying to a coffer-dam. This will be alluded to in another 
paragraph. 

II. In whatever manner the coffer-dam maybe constructed, 
with or without the puddle, the first step is to pump out 
the water This can be done by any of the ordinary pumps, 
such as the force, lift, or centrifugal pump. A single pump 
discharging a stream of from 4 to 10 inches in diameter should 
always be sufficient to keep the water out of a coffer-dam, and 
will ordinarily prove sufficient ; but if the dam is badly con- 
structed, or unexpected and large leaks are developed, it may 
require several pumps. There are two forms of the centrifugal 
pump : one in which the vanes are in a horizontal casing which 
is placed at the bottom of the excavation, and is lowered as the 
excavation proceeds, the discharge connected with this, and 
lengthened as required ; this forces the water upwards and dis- 
charges it over the top of the dam ; in the other the vanes are 
in a vertical casing, and is generally placed on or near the top 
•of the dam ; a pipe extends to the bottom of the excavation and 



TIMBER FOUNDATIONS. 157- 

is lengthened as required ; this lifts the water to the top and dis- 
charges it over the dam. Either of these pumps will throw a. 
6 or 10 inch stream, and should be ample for any dam properly 
constructed. The force-pump is placed either on top of the dam, 
or at the bottom of the excavation, or at any intermediate point,. 
and will throw any diameter of stream required. The force- 
pump is apt to give more or less trouble by the accumulation of 
small fibres of wood, leaves, or small gravel and sand in the valves 
and between the sliding plates, causing delay and frequent stop- 
ping of the pump, often at a critical period of the work, no mat- 
ter how carefully the suction end of the pipe may be protected by 
screens and strainers. In all important works duplicate pumps 
should be on hand, unless they can be obtained without delay, 
as the stoppage of a work of this kind might cause a suspen- 
sion of the work for a season, or the breaking and loss of a 
coffer-dam. A centrifugal pump is less liable to get out of 
order, as it will readily discharge small chips, sand, and grit 
without damage or stoppage to the working of the pump. 
(Plate V, Figs. 1, 2, 3, and 4.) 

12. When the water is pumped out, and no serious leaks, 
have developed, the excavation of the bottom can be com- 
menced. The material, as far as practicable, should be kept 
piled up against the sides of the dam, and if the proper area 
has been enclosed there will be little danger of undermining 
the dam, or of forcing in the sides of the dam by the outside 
pressure, when the distance from the water-level to the bot- 
tom of the excavation does not exceed 25 feet, and this with- 
out interior bracing, in a double-wall puddle-dam. Braces 
should always be omitted, if possible (but in all cases timber 
should be kept in convenient positions, and of proper lengths, 
so that they can be readily and rapidly used if any signs of 
yielding are observed), as they materially interfere with and 
delay the construction of the masonry. A few braces placed 
diagonally across the corners of a rectangular-shaped dam will 
add greatly to the strength of the dam, and will be practically 
no obstruction to the work. It will be found advisable, both 
to limit the amount of excavation, increase the space on which 



158 A PRACTICAL TREATISE ON FOUNDATIONS. 

the excavated material can be deposited on the inside of dam, 
and at the same time increase the height to which it may- 
be piled against the side of the dam, to place a row of 
timber around the area to be occupied by the masonry, leav- 
ing a small margin all around, and then to drive sheeting be- 
hind this. As the excavation proceeds drive the sheeting 
farther down. In a large coffer-dam in the Ohio River the 
writer placed a double row of 12 X 12 inch timbers around the 
area required to be excavated, as soon as the water was 
pumped out. On the outside of this a 3-inch plank was bolted 
so as to leave a space of about 4 inches between the timber 
and the plank. Sheeting plank from 6 to 8 feet long was 
then driven two or three feet into the bed of the river. This 
provided a space of about 6 feet all around upon which the 
excavated material could be deposited. As the excavation ad- 
vanced a man was kept driving the sheeting down. The plank 
bolted to the square timber prevented the upper end of the 
sheeting from inclining outward, and consequently the lower 
ends from pressing inwards, and the excavation continued 
through about 8 feet of gravel and sand to the clay. By this 
simple arrangement the excavation was confined to the exact 
area required. The material was simply cast by the shovel 
against the sides of the dam, both of which reduced the cost 
greatly, and the dam was well supported from the inside. 
Leaks were almost entirely prevented, and not a brace was 
used from the beginning to the end. The depth from the 
water-level to the bottom of the excavation was about 23 feet, 
the length of this coffer-dam on the inside 60 feet, and width 
34 feet. The thickness of the sides of the dam was intended 
to be 8 feet, but, owing to careless driving of piles, it was not 
more than 6 feet in places. The thickness of the puddle itself 
varied from 2\ to 5 feet. 

13. In another dam somewhat carelessly constructed, and 
which showed evident signs of weakness, of about the same 
-size as the above, but requiring a wider and longer pier, an 
inner crib was constructed, while the dam was filled with water, 
as follows : Horizontal timbers were framed together so as to 



TIMBER FOUNDATIONS. 1 59 

enclose a space somewhat larger than the bottom area of the 
masonry. The bottom layer was cut diagonally, so as to form 
a cutting edge. Another 12 X 12 inch layer was bolted to this. 
3-inch plank 8 feet long was then spiked on. At the corners 
and at intervals on the sides and ends, posts 12X12 inches X 
4 feet were placed vertically on the horizontal pieces, to 
which the plank was spiked. On the posts another course of 
horizontal timbers was placed, and so on until the crib rested 
on the bottom. The space between the crib and coffer-dam 
was then filled with earth. The water was then pumped out. 
A few braces were placed on the inside of the crib ; the ex- 
cavation was then commenced, the crib, weighted with large 
stone, settled gradually. After excavating a few feet, the 
coffer-dam commenced to be undermined ; the material between 
crib and coffer-dam commenced to flow to the interior. The 
sides of the dam bulged inwards until they rested against the 
crib. The puddle in the coffer-dam settled ; the pumps could 
not keep down the water. It was decided to flood the dam for 
fear that the crib-dam and braces could not stand the pressure. 
After carefully considering the conditions, two plans presented 
themselves. One was to build a new dam ; this would take a 
long time, cost a great deal of money. The other was to re- 
puddle the old dam, and also to throw a large quantity of 
puddle around the old dam on the outside, pump the water 
out, and then brace strongly the crib, and endeavor to reach a 
safe foundation, the inner crib holding the coffer-dam in place. 
This was the most expeditious, and seemed practicable, if we 
could pump the water. This was decided upon and acted 
upon at once. The water was again pumped out. Bracing 
the crib strongly as the water fell. The dam rested hard against 
the crib in places, creating great frictional resistance, requiring 
a largely increased weight to sink the crib. The excavated 
material was placed between the crib and the dam ; it would 
continually flow back. Such material as was not placed be- 
tween the crib and dam was lifted out in buckets and dumped 
into the river. In this manner, with much delay, and with 
slow progress, we succeeded in reaching the clay upon which 



l6o A PRACTICAL TREATISE ON FOUNDATIONS. 

the structure was built, after excavating through 14 feet of 
gravel and sand. This inner crib has the following advan- 
tages : 1. It reduces the amount of material to be excavated to 
a minimum, saving time and money. 2. It enables us to keep 
the lower part of the main and sheet piles always covered, pre- 
venting undermining of the dam, and great inflow of water, 
sand, and gravel, by keeping the space between the dam and 
crib always filled with material. 3. The crib can be sunk even 
below the points of the main or guide piles without danger. 
The space between the crib and dam should not be less than 
5 or 6 feet. Great depths can be reached by this means, and 
the crib should always be used if the depth is over 20 to 25 
feet. The crib can be built up as the excavation and sinking; 
progresses. (See Figs. 1, 2, 3, and 4, Plate III.) 

14. In many cases a crib of this kind can be used without 
any puddle-dam on the outside. This would require the plank 
sides to be calked to prevent too great an inflow of water. 
A modification of this construction is used as a coffer-dam, for 
the sides of the open caisson, or on top of a pneumatic caisson, 
and of heights from 20 to 40 ft. This will hereafter be ex- 
plained and illustrated. 

15. The puddle filling in coffer-dams is generally composed 
of such earth as is easily accessible. Some materials are better 
than others, but any ordinary clay or loam will make good 
puddle if the layers are well bonded or cut into each other. 
What is known as brick-clay makes an excellent puddle. Some 
high authorities recommend a sand and gravel filling, which is 
claimed to be better than clay ; and should a large leak occur, 
the sand and gravel will fall and fill the cavity, and can be re- 
filled on top. This is true ; but water will always find its way 
through sand and gravel, where, if well mixed with clay, or clay 
alone, it is practically impervious to water. The writer pre- 
fers greatly this last material. 

16. Coffer-dams generally prove to be expensive, are always 
uncertain, and, unless sufficiently large, or some form of inner 
support used as above described, will give trouble, frequently 



TIMBER FOUNDATIONS. l6l 

filling up with water and earthy material, or undermining, and 
not unfrequently breaking in. / 

17. Sometimes coffer-dams are used when it is intended to 
drive piles in the enclosed space for the foundations, no/ma- 
terial being removed from the bed of the river, but simply to 
keep the water out while the piles are being cut off an\d a 
timber platform framed on top. This platform consist:! of 
several courses of square timber. The piles being cut off at the 
same level, they are then capped by 12 X 12 in. timber, thten 
another course at shorter intervals placed across and at right 
angles to the caps, and over this another course of square tim- 
ber placed close together, forming a solid timber floor, the 
whole thoroughly bolted together with drift-bolts. The open 
spaces are sometimes filled with broken stone or concrete, 
around the tops of the piles, between and under the timbers; 
this is not necessary unless the material is very soft or yielding, 
and is only intended in this case to give lateral stiffness and 
steadiness to the piles ; or the timber platform may be omitted, 
and a thick bed of concrete placed around and over the top of 
the piles. 

18. If the material has been removed to the proper depth, 
the bed of gravel, sand, or clay is levelled. The masonry may 
be commenced directly on these materials, but it is better to 
first lay a bed of concrete not less than 2 to 3 feet in thickness 
over the area, and extending a distance equal to the thickness, 
outside of the space to be occupied by the masonry ; or a course 
of square timber may be laid on the foundation-bed ; or the 
two may be combined, timber being embedded in the concrete. 

19. Coffer-dams are rarely used where the material has to be 
excavated to any great depth, for the reasons above described. 
Some other method will be in general preferred, such as the 
open caisson. 



102 A PRACTICAL TREATISE ON FOUNDATIONS. 



Article XXXI. 
OPEN CAISSON. 

20. AN open caisson is simply a water-tight box open at 
the upper end, and is constructed as follows : A floor of square 
timber, \2 X 12 in., built of two or more courses of timber, 
well bolted together, and of any size and shape, but from 
4 to 6 ft. larger than the proposed structure ; this floor is to 
be thoroughly calked. Near the outer edges of this, large 
bolts with eyes are fastened ; about one foot inside of the bolts 
square timber sills 12 X I- in. are placed ; vertical posts 12 X 12 
in. are connected to these by mortise-and-tenon joints. On 
the top of these posts, which are placed from 4 to 5 ft. apart, 
caps of 12 X 12 in. timber are placed and secured; these 
skeleton frames are then covered by two courses of sheeting 
plank, the inner course placed diagonally, the outer course 
horizontally; over the top of the sides 12 X 12 in. pieces are 
placed, projecting over the sides and ends not over 1 to 1^ ft. 
Long iron rods with hook at one end and screw-threads at the 
other are hooked to the eye-bolts and passed through holes in 
the top pieces ; a washer is placed on top, the nut being 
screwed on so as to bring the sides to a hard bearing on the 
floor or platform. These sides can be of any height, but it is 
best to use a height of not more than 15 to 20 ft. at first, and 
when sunk to this depth add another section similarly con- 
structed on top. In this case a thimble or sleeve with right- and 
left-handed threads should be used instead of the nut on the 
end of the rod, so that other sections of rods can be connected 
as the sections of the sides are added. As soon as the sides are 
brought to a firm bearing on the floor the outside planking 
should be thoroughly calked. 

21. The caisson is now ready to be floated to the site of 
the structure. A course or two of masonry should be laid to 
steady the caisson and prevent any tendency to careen or turn 



OPEN CAISSON. 163 

sideways. If the bed of the river is of a firm material— clay, 
sand, or gravel— it is only necessary to level the bed. If there 
is danger of scouring when the current is strong, or the ma- 
terial is too soft to bear the load, piles must be driven and 
then cut off to a level cither at the bed of the river or at some 
point below the water surface. In either case the building of 
the masonry is continued until the caisson nearly reaches the 
bed of the river or the top of the piles, as the case may 
be. The caisson carefully adjusted or located in its exact 
position by ropes attached to anchors or to guide-piles driven 
for the purpose, enough water is now let in to complete the 
.sinking. If it does not rest in a level and easy position, or 
veers out of place, the water is pumped out, the caisson lifts, 
the bed or piles properly levelled, and the caisson again sunk ; 
and this must be repeated until the result is satisfactory. In 
the case of resting on piles, a diver should be sent down to see- 
that it rests practically on all the piles, as with a light load it 
might be supported by only a few piles, and the increased 
weight would cause the piles to sink ; but even in this event 
the only effect would be to settle until other piles were brought 
into a bearing, and any increase of height of structure can be 
supplied by the courses of masonry. Any number of piles can 
be sawed off under water so as not to vary in level more than 
one-quarter inch ; this difference can cause no harm. The 
structure can then be completed. When this rises above the 
water surface the iron rods can be unhooked and removed ; the 
sides of the dams can then be lifted and used on other piers. To 
enable this to be done the corner posts are made in two pieces 
and held together by a pin-bolt, which can be removed, and 
the sides and ends easily fall apart. The sides of the dams 
should be braced against the masonry by short blocks as the 
caisson sinks. It will hardly prove economical to use the sides 
over again, unless timber is scarce or costly. The manner of 
cutting piles off under water will be explained under head of 
Piles (Plate IV, Figs. 1 and 2, also Plate V, Figs. \a and 2a). ^ 
22. In depths of water not exceeding 20 to 25 feet this 
method of construction is simple and economical. The bottom 



164 A PRACTICAL TREATISE ON FOUNDATIONS. 

of the caisson forms a part of the permanent structure. The 
masonry is being built up as the caisson sinks, Avhich is not 
the case in a puddle coffer-dam. The material can be cheaply 
excavated and levelled by dredging, providing that a dredging 
machine can be hired at a reasonable cost, or enough of it is 
to be done to justify a contractor to undertake the work. 
These sides are properly a single-wall coffer-dam, calking 
being substituted for the puddle, and interior bracing used 
instead of thickness of dam to secure strength and stability. 



Article XXXII. 

GUSHING GYLINDER PIERS. 

23. THESE piers are constructed as follows : A cluster of 
piles is driven, to a solid bearing or to a satisfactory resistance,, 
as close together as practicable, and in juxtaposition,* if it can 
be done; each cluster is composed of from 4 to 12 piles, 
bolted together strongly at or near their upper ends. The 
piles should be straight and of good size, not less than 12 
inches square or diameter at large, or less than 9 or 10 inches- 
at smaller end. In driving such clusters the pile should be 
slightly inclined or raking while being driven, and the tops 
subsequently pulled together and held by bolts. The piles, 
should penetrate the soil not less than 20 feet, and as much 
more depending on the nature of the material as to softness or 
hardness, and should reach well below any danger from scour- 
ing action. Iron cylinders from 4 to 10 feet in diameter 
should then be sunk around the piles at least to a depth of 10 
feet below the bed of the river. These cylinders are made in 
sections of from 5 to 10 feet in length and of a thickness from 
1 to ItV inches of metal, with internal flanges about 3 inches wide. 
The lower edge of the bottom section should be brought to a 
feather or cutting edge. Cast-iron is generally used. Enough 

* The same number of piles, if driven at small intervals apart, would carry 
greater loads, as a larger aggregate area of surface would be available for fric- 
tional resistance, but require larger cylinders. 



CUSHING CYLINDER PIERS. 1 65 

of these sections are bolted together to reach from the bed of 
the river to a point above the water surface. This being 
placed around the pile clusters, another section is bolted on. 
The material is then removed from the inside or stirred and 
loosened so that the cylinder will either sink by its own weight 
or by adding weights on top. When it reaches the proper 
depth, the interior of the cylinder is filled with concrete. The 
water may be pumped out if the material at the bottom is 
clay or silt, and in some cases if of compact sand ; but com- 
monly the water remains and the concrete is simply thrown 
in. When filled a thick iron cap from 2^- to 3 inches thick is 
bolted to the top. For that portion of the cylinder above the 
bed of the river the flanges can be cast on the outside. Two 
of such cylinders and pile clusters, bolted and braced to each 
other at the proper distance apart, constitute a pier. Four 
may be used to a pier, which greatly increases the stability. 
A two-cylinder pier, if it stands any great height above the 
bed of the river, is wanting in lateral stability ; and if the ob- 
struction caused by the piers causes any scouring, the safety 
of the structure is greatly endangered, calls for frequent ex- 
amination, and requires for security the constant and liberal 
use of riprap or broken stone around the cylinders. The piles 
should be cut off at or below low water. In this form of pier 
the piles are the real supporting power. The concrete carries 
the load from the structure above to the piles; the cylinders 
merely serve as a casing to hold the concrete. If in sand or 
gravel, the friction on the sides of the cylinder will give some 
additional support. These piers are economical, easily and 
rapidly constructed, but are wanting in stability. (See Plate 
IV, Figs. 7 and 8.) 

24. In many cases, both for railroad and highway bridges, 
the piles are omitted ; the cylinders are sunk into the material 
anywhere from 3 to over 100 feet, and are then filled with con- 
crete. In such cases the cylinders are of large size for railroad 
bridges, are generally larger at the bottom, and taper or batter 
to the top. They are capable of bearing heavy vertical loads, 
•are wanting in stability, especially if subjected to heavy lateral 



1 66 A PRACTICAL TREATISE ON FOUNDATIONS. 

pressures resulting from moving ice and drift in large masses r 
or exposed to great and repeated shocks. Their cheapness 
has led to a frequent use for highway bridges and compara- 
atively short spans. Some examples will be given in another 
paragraph of such piers, with methods of sinking, dimensions,, 
heights, etc. 

Article XXXIII. 

SOUNDINGS OR BORINGS. 

25. THE importance of a thorough knowledge of the mate- 
rial underlying the site of any proposed bridge is so evident 
and great that it would seem unnecessary to more than allude 
to the subject ; but the fact is that engineers, from a notion of 
false economy, neglect to gain the necessary information, and 
as a result design and prosecute the construction of even im- 
portant structures either ignorant or at least with but very- 
meagre knowledge of the nature and lay of the strata, and 
when too late find themselves involved in difficulties which 
will cost thousands of dollars to overcome, which could be 
saved by the expenditure of not over two to three hundred 
dollars, expended in judicious and thorough soundings, to say 
nothing of the delay and stoppage of the work. Thorough 
sounding will always be money well spent and time saved. 
For these reasons this subject will be explained in some detail- 

25I. The first and usual method is simply to drive an iron, 
rod or pipe from I to 1^ inches diameter. A rod of this kind 
can sometimes be driven to a depth from 10 to 30 feet by con- 
stant hammering and turning after each blow. The informa- 
tion, however, obtained is meagre and unsatisfactory ; the 
character, thickness, or lay of the different strata penetrated 
cannot be determined ; boulders, even small ones, will stop 
the driving, as will also logs or drift or wrecks. Reports 
based upon such soundings lead to erroneous conclusions ;. 
designs, estimates, and contracts are made that require change 
and alterations, involving often largely increased, cost and 
delays. In one important bridge across the Ohio River, plans,. 



SOUNDINGS OR BORINGS. l6? 

estimates, and contracts were closed on the supposition that 
rock would be reached at a short depth, and this information 
was apparently confirmed by the fact that another bridge in 
sight was built on rock at a short distance below the water 
surface ; but subsequently it was discovered that no firm 
material existed under from 60 to 70 feet below low water, and 
the foundations had to be constructed by the pneumatic 
process. Every engineer knows the cost of such a change in 
the conditions and terms of a contract. 

26. A better and more satisfactory method is to sink a terra- 
cotta or iron pipe from 3 to 8 in. in diameter, as follows : The 
pipe is pressed into the surface as far as practicable ; then a 
long narrow bucket with a cutting edge, and a flap valve a little 
distance above the cutting edge opening upwards, is dropped 
into the pipe and is alternately and rapidly raised and dropped. 
The material will be collected in the bucket, and at intervals 
the bucket is lifted entirely out and the contents of the bucket 
are emptied. This is repeated ; the pipe will gradually sink, a 
man standing on top if it is necessary. Other sections of pipes 
are added from time to time. It will be necessary sometimes 
to pour water into the pipe to aid in the cutting and flow of 
the material into the bucket. The bucket should be connected 
by a rope passing over a sheave connected with a frame or 
shears above. Great depths can be reached by this method 
with reasonable rapidity, and at no great cost. The writer 
used this on the Ohio River with satisfactory results. It 
enables you to determine the thickness and nature of the 
strata; that is, you can determine whether the strata is sand 
or gravel or clay, but you do not know in what condition it 
exists. Clay will be brought up in the condition of mud. The 
strata may contain a large quantity of water, which would 
render it unsuitable for a foundation-bed when the overlying 
strata are removed. An experienced well-borer can form a 
good opinion on these matters. On the whole much valuable 
and satisfactory information can be gained, and it is greatly to 
be preferred to the rod process. The rod will often bend above 



1 68 A PRACTICAL TREATISE ON FOUNDATIONS. 

or below the ground, and this often misleads, as the bending 
apparently renders the depth actually penetrated uncertain. 

27. The third method is simple, relatively inexpensive, and 
entirely satisfactory. All that is needed is a number of sections 
of pipe, i^ in. diameter and f in. diameter, a small hand force- 
pump, and a small barge or raft. Threads are cut on both 
ends of every section of pipe, and a number of thimbles with 
internal screw-threads to fit. A chisel-steel wedge-shaped 
section about 1 ft. long, with two small holes passing through 
the faces of the wedge into a hollow tube, made to fit the f-in. 
pipe. An upper section also about a foot long has a solid 
handle at right angles ; a short hollow elbow is connected with 
this, to which a hose from the pump can be connected. 
Enough sections of the i^-in. pipe are connected together to 
reach from the surface of the water to the bed of the river. 
This pipe is lowered to the bottom and pressed 4 or 5 ft. in 
the bottom ; the top is then secured to the boat or raft. When 
the water is deep and the current is rapid, this pipe is liable to 
bend considerably, and might part at some joint. A rope at- 
tached to a small anchor and to the pipe at some point below 
the water will relieve this, the anchor being dropped well up 
stream. The f-in. pipe is now connected together with the 
chisel end at the bottom and lowered in the if-in. pipe; the 
hose then connects the smaller pipe with the pump. The 
pump is started ; the water rushes through the small apertures 
at the bottom, and passes upward between the two pipes, 
bringing the material of the bottom with it, which is discharged 
at the top. The small pipe is turned, and easily works its way 
into the soil. The larger pipe would also settle with it ; but 
this is not necessary, and is fastened at the top. At intervals 
of 4 or 5 ft. the inner pipe can be lifted entirely out, the chisel 
end removed ; a tube of iron or brass a foot long, slightly con- 
tracted at the lower end, of the size and shape of the straight 
cylindrical lamp-chimney, is now screwed to the small pipe, 
lowered to the bottom of the hole, and pressed 1 foot into the 
bottom, then lifted out again. The material in the brass tube 
can now be pressed by means of a round stick into a lamp- 



SOUNDINGS OR BORINGS. 1 69 

chimney, a piece of thin sheet rubber fastened over the ends. 
We have now a cylindrical specimen of the material at that 
depth in the exaet condition in which it existed in the strata ; 
this will retain its moisture for a long time. This is, however, 
only practicable in clay, silt, or mixed soils. In these materials 
t»he hole will remain, and the pipe can be lowered to its bottom 
without letting the larger pipe follow. We have often bored 
40 to 50 ft. in a day. When in a bed of loose sand and gravel, 
the water will not return upwards through the annular space 
between the pipes, but will escape laterally at the bottom, so 
that the material cannot be brought to the surface, but the 
water will so loosen it that the pipe will readily sink. It should, 
however, be turned constantly and rapidly, and be lifted a short 
distance occasionally ; otherwise the sand and gravel will rise 
up between the two pipes, or compact above the chisel section 
and bind the pipe, increasing both the difficulty of sinking or 
raising the pipe, and causing sometimes the loss of the smaller 
pipe. It is better in this material to let or make the larger 
pipe follow the smaller one, but it is not necessary. The only 
skill required in this method of boring is to prevent this bind- 
ing. In silt there is danger of the pipe sinking too rapidly, which 
would also bind the pipe ; constant turning and frequent lifting 
will prevent it in either case. If bowlders are encountered, or 
logs either, they can be readily drilled through, as the pipe is 
free to be lifted and dropped. Rock is easily determined either 
by hammering on the top of the pipe or lifting it and letting 
it drop ; the rebound or the sound either enables you to dis- 
tinguish between solid rock and bowlders. The entire outfit is 
cheap ; any plumber or mechanic can make the connections 
necessary with the ordinary gas or water pipes in common use. 
Two or three men can perform all of the work required. This 
method was used in all of the piers at the Susquehanna River, 
Schuylkill, and Tombigbee, and Ohio River at Louisville, in 
depths varying from 40 to over 100 ft. A single boring at the 
site of a pier is not enough ; at the Susquehanna and Schuylkill, 
from six to ten soundings were made at the site of each caisson, 
one at each corner, and one or two intermediate along the 



170 A PRACTICAL TREATISE ON FOUNDATIONS. 

sides, and if any great or abrupt irregularities were developed 
additional borings made. From this an exact diagram of the 
lay of the bottom, in reference to the surface of the water and 
bed of the river, was made. We knew in the beginning the 
exact nature of the material to be passed through, the high 
and low points of the rock and the exact depth to each, and 
the exact amount of material to be excavated. The position 
of each sounding was located accurately by triangulation or the 
wire measurement from an established base. At the Susque- 
hanna a good part of the boring was done in the winter, when 
the river was solidly frozen over. The information thus ob- 
tained cost a very small sum, and was invaluable. (See Fig. 
10, Plate IV.) 

Article XXXIV. 

TIMBER PIERS. 

28. Where stone or brick is hard to obtain, or costly on 
account of the long distances over which it must be hauled or 
transported, or when it is important to erect a bridge without 
the delay incident to constructing masonry piers, it becomes 
necessary to build timber piers. These piers are generally so 
designed that masonry or iron piers can be easily and con- 
veniently constructed at some future time. Two types of such 
piers, constructed by the writer, will be briefly described and 
illustrated. In building a railroad across the swamps in 
Alabama between Tensas and Mobile, a number of bayous or 
streams had to be crossed ; these being navigable, many draw- 
bridges had to be constructed, large enough to pass the large 
steamboats navigating the main rivers. The pivot or centre 
piers were constructed by driving a number of piles 2\ ft. cen- 
tres over a square area of the proper size ; , these piles were cut 
off a few feet above the water surface, were capped with 
12 X 12 in. square timber and bolted to the piles with drift 
bolts 1 in. square and 2 ft. long. Upon these, and at right 
angles to them, other timbers were placed at about one foot 



TIMBER PIERS. Ifl 

intervals, and upon these a solid flooring of square timbers ; 
these timbers were connected by i-in. screw bolts with 2-ft. grip 
— that is, length of bolt between timber surfaces; the entire 
length from out to out of bolt, included head, nut, and washers, 
would be 2 ft. 3! in. This completed the pier ; the upper 
surface was then planed to a level, to receive the turn-table 
arrangements. The number of piles required varied from 49/ 
to 81, according to the size of the piers, and were driven from 
30 to 40 ft. into the bed of the stream, which was composed 
almost entirely of a soft silt or mud. The rest-piers were com- 
posed of three rows of piles, about 3 ft. apart, from 5 to 6 piles 
in each row ; these were capped with three courses of timber, 
as in the pivot pier ; upon this flooring other timbers were 
placed to support the latch beam for the ends of the draw span, 
and for the support of the stringers of the trestle approach- 
These piers were now complete ; they were constructed in a 
few days and at a small cost. It was an easy matter at some 
subsequent time to cut the piles off below low water, and to 
build brick piers on them ; this has been done. 

29. The following is another form of timber pier carrying 
spans from 100 to 120 ft. Sixteen piles were driven in two rows,, 
eight piles in each row. The distance between the rows was 
regulated, as in masonry piers, by the size required at the top, 
and allowing for the batter. The distance between the piles 
in each row was regulated by placing the piles to the best ad- 
vantage for supporting the structure above, as will be seen in 
the drawing; these were then capped with 12 X 12 in. timber,, 
upon which were placed other timbers at right angles to the first,, 
all bolted and fastened together by iron straps. Upon this plat- 
form a strong double framed-trestle was erected, constructed 
of eight vertical and inclined posts, with cap and sill ; on these 
cross-pieces were placed, and then a platform for the bridge to* 
rest upon. All timbers were 12 X 12 in. square, the whole 
structure well tied together, and braced longitudinally. See 
drawing, Figs. 1, 2, and \a, Plate VI. Such a structure will 
bear a heavy load, is however, temporary in its nature, is 
very light, and is wanting in stability if liable to be subjected 



'«72 A PRACTICAL TREATISE ON FOUNDATIONS. 

to severe shocks. In this case a timber starling or cut-water 
should be constructed at the up-stream end, either built en- 
tirely separate from the pier itself or forming a part of it. 
Extra piles can be driven triangular in plan, and resting upon 
these large square timbers should be placed, inclining at a 
rather flat angle to the body of the pier; this should be 
close-sheeted with plank, and filled in part or entirely with 
broken stone or gravel, or better with concrete — in which event, 
when the timbers rot, a permanent concrete pier would remain. 
Either pine or oak timber is well suited for such structures. 



Article XXXV. 
FRAMED TRESTLES. 

30. TRESTLES are used to carry a railroad over swamps, 
Tivers, or creeks, when material for making embankments is 
'difficult to obtain. In building over low places, a simple 
framed trestle composed of a cap, sill, and four posts, two placed 
vertically under the rails and one on either side inclined to the 
verticals, with a batter of about 3 in. to each vertical foot. 
This frame ordinarily rests on mud sills, which are simply 
short pieces of square timber 5 or 6 ft. long, partly imbedded 
in the soil, or better on small rubble-masonry pedestals. All 
timbers in these frames or bents are generally 12 X 12 in. tim- 
ber ; the batter posts are sometimes 10 X 12 in. square. Diag- 
onal bracings, called X-bracing, are then placed passing diago- 
nally from the top to the bottom of the bent on both sides, 
■made of 3-in. X 9 or 12-in. plank, and bolted to each post. 
Spikes are often used; bolts cost but little more, and are much 
better and ultimately more economical. If the bents are very 
iiigh, longitudinal braces either of 3-in. plank or 6 X 6 in. square 
timber are placed from bent to bent and bolted to the posts. 
The bents are placed generally from \2\ ft. to 14 ft. centre to 
centre. Where a greater height than 25 ft. is required for the 
foents, they are built with one, two, or more stories, each of a 



FRAMED TRESTLES. IJ £ 

height not exceeding 20 ft., the upper section resting on top of 
the next lower, and so on to the bottom, the posts in each section 
framed so as to be in the prolongation of those in the sections, 
above, and additional verticals or inclined pieces are introduced, 
in the lower sections, the whole thoroughly bolted and braced-, 
together. In the form of trestle just described, the vertical: 
posts are supposed to carry the greater part of the load, the 
batter or inclined posts mainly intended to give a wide base 
and lateral stiffness to the bent. This is the actual case, when*. 
the top of the batter post is a foot or more from the top of the 
vertical. When placed close together both posts bear a part ol 
the load. In order to give stiffness and at the same time to* 
make all posts bear an equal share of the load, all of the posts, 
are inclined at or about the same angle ; this is called the M- 
trestle ; two posts touching at top and inclining downwards in 
opposite directions are placed under each rail, the inner posts, 
coming together at the bottom in the middle ; the outside posts 
may have a little greater batter than the inner ones. In this 
manner the load is distributed over and borne by four instead 
of two posts. In this form of trestle the posts need not be more 
than 9 or 10 X 12 ins. square ; but unless the amotfnt of timber 
required is very great, as in very high and long trestles, the 
timbers are not proportioned to the loads they have to bear, as. 
the amount of material saved would be of little moment. In, 
very high trestles, such as two, three, or more stories, economy 
requires the bents to be placed farther apart, the timbers hie 
the bents remaining from 10 to 12 X 12 ins. square. In- 
high trestles the bracing and some of the auxiliary or second- 
ary members are of smaller scantling or plank. The drawings,., 
showing in detail the types of the different trestles and the 
dimensions of the several members used, there will be no need 
of a lengthy description. (See Figs. 3 and 4, Plate VI.) 

31. It will be sufficient to say that the upper cap need not; 
be over 10 or 12 feet long. The intermediate sills (which are 
a sill to the section above and a cap to the section below) are 
equal to the length of the cap increased by 6 inches for each, 
vertical foot between them, to these the posts are connected^ 



174 A PRACTICAL TREATISE ON FOUNDATIONS. 

by the mortise-and-tenon joint, or by drift-bolts or iron straps, 
— commonly by the first method. Some engineers use two 
ntermediate pieces, so that each section is a separate and in- 
dependent frame, in which case the longitudinal braces are 
framed between the two. There seems to be no decided ad- 
vantage in this, and it requires more material, and consequently 
more cost. The bottom sill will be equal to the top cap in- 
creased by 6 inches multiplied by the total height of the tres- 
tle. All the main posts should be in lengths of about 20 feet, 
except the bottom section, which is generally less than 20 feet, 
often not over from 5 to 10 feet. The longitudinal braces are 
from 6x6 inches to 6 X 8 inches square, and the same for 
the secondary members. The diagonal bracing is generally 
3-inch plank, 9 to 12 inches wide. (See Plate VII, Figs. 1, 2, 3, 
and 4.) 

32. Whatever may be the height and form of trestle-bent, 
and whatever distance apart, there are placed on top of the cap, 
stringers, extending longitudinally and at right angles to the 
cap, one stringer under each rail, and commonly placed di- 
rectly over a post. Each stringer is made of two pieces for 
bents 12^ feet centres. They are 6 X 14 inches cross-section 
each, and should be 25 feet long. They are placed side by 
side with a 2 or 3 inch space between them, and bolted to- 
gether by screw-bolts, blocks of wood or cast-iron spools being 
placed between them, through which the bolts pass. These 
bolts are from f to f inch diameter, with cast-iron or wrought 
plate washers, and nuts to suit. Four bolts are used over each 
cap, and sometimes two or more between the bents, for each 
packed stringer, and one bolt from | to 1 inch diameter to 
bolt the stringer to the cap. This bolt has to be slightly 
inclined so as to pass the end of the post below. For bents 

14 to 15 feet apart, packed stringers 7X15 inches or 8X15 
inches are used, and if practicable to obtain them they should 
be 28 or 30 feet long; but if not practicable, lengths of 14 or 

15 feet can be used. But this requires a bolster, that is, a 
piece of timber 8 to 10 inches thick, 4 to 5 feet long, placed 
«on the cap and bolted to it. The stringers then rest on the 



FRAMED TRESTLES. 1 75 

bolsters, to which they are bolted. In this case the stringers do 
not break joint on the caps. It does not form as stiff a trestle 
as when the joints are broken, but will answer every purpose. 
Pieces of timber bolted to the side of the stringers and rest- 
ing on the cap can be used instead of the bolsters. (See Plate 
VII.) 

23. For spans from 15 to 25 feet it is economical to use 
stringers of the same cross-section as above, but they should be 
strengthened below either by struts resting on the bents at the 
lower end and at the upper end against straining-pieces— these 
are pieces of timber bolted to the stringers underneath and near 
the centre, these pieces being 5 or 6 feet long, and 6 or 8 inches 
thick — or by iron rods passing through the stringers at the ends, 
and under a block of wood or a short iron strut placed under 
and at the centre of the length of the stringer. Either of these 
constitute a trussed beam. The stringers in this case can be 
either of two or three pieces packed together. Sometimes, in- 
stead of trussing the stringers as above, an increased number of 
pieces can be used. Four pieces of timber 12 X 12 inches 
square, bolted together with bolts and packing-blocks, which 
are framed into the sticks so as to act as keys, will be amply 
strong for a span from 20 to 25 feet ; or two pieces laid side by 
side, and another single piece on top, will do for a span from 
15 to 20 feet. These are mere expedients, have a bad distri- 
bution of material, and make a heavy, bungling-looking job. 
See Figs, ia to 6a, Plate VIII.) 

34. On top of the stringers the cross-ties are laid. These 
are 6x8 inches square, and from 8£ to 9| feet long, are gen- 
erally spaced from 12 to 16 inches centres, and spiked to the 
stringers. It is poor economy to space the ties with too great 
intervals. If a train runs off the track the wheels sink in the 
space between the ties, and before the momentum can be 
overcome, the trestle will be torn to pieces, and not unfre- 
quently the train will be badly wrecked. If the ties are not 
over 2 or 3 inches apart, the train can easily run on the ties 
without serious damage to either train or trestle. On top of 
the ties and near their outer edges guard-rails (longitud- 



176 A PRACTICAL TREATISE ON FOUNDATIONS. 

inal pieces of timber 6x6 inches or 6 X 8 inches) are placed 
and bolted to the ties. A common rule is to use a £-inch 
screw-bolt at every fifth tie, and spikes between the bolts. 
The guard-rails are sometimes cut or " dapped " to the depth of 
an inch, a tongue projecting down between the ties. What- 
ever theoretical advantage may exist practically as the work is 
done, there is no advantage whatever gained. The writer 
thinks that the guard-rail had better be placed inside and 
close to the rail, not over two or three inches from the rail. 
In this case the top of the guard-rail should not be above the 
iron rail of the track. It might be placed both inside and out- 
side. This completes the trestle. The cross-ties on trestles 
and bridges are always sawed. On embankments they are 
hewn. It is claimed that a hewn tie will last longer than a 
sawed tie. No good reason seems to be assigned for this. 
The hewn tie is almost universally used on embankments, as 
they are generally cut and hauled from the woods adjacent to 
the line, carried by trains to point where used ; smaller trees 
are used, which are younger and more vigorous than those 
which are larger and on the decline, and which have to be 
split through the centre. In the piney woods of the South 
dead-wood trees, either standing or fallen, are largely used for 
ties, and are said to be equally as good as, if not better than, 
green-wood ties, as the sap is either rotted or is easily removed. 
Oak ties, either white oak or post oak, are preferred to the 
pine ties. They are not so rapidly cut into by the rail, this 
cutting tending to cause rot in the tie under the rail, and they 
hold the spike better, owing to their hardness ; but, on the 
contrary, they warp and split to a greater extent than pine,, 
which admitting and holding water causes internal rot. Oak 
ties cost about 10 cents more than pine ties, 40 cents and 30 
cents, respectively, being average costs. Pine is generally used 
where it is abundant ; oak, where it is abundant. The same 
may be said in general of the other timbers of the trestle. 
But probably pine is preferred for caps, sills, and posts. It is 
more easily cut and framed, has great strength and durability, 
does not warp, split, or crack as readily as oak, and can be 



FRAMED TRESTLES. 1 77 

obtained in longer and straighter sticks. Oak is somewhat 
stronger and heavier. Either will answer in any framed struc- 
ture. Cost and rapidity of supply alone are factors worth 
considering in deciding between the two. 



Article XXXVI. 

QUALITIES OF TIMBER. 

35. In the North white pine is abundant, and is used for 
all purposes in framing. It is soft and white, easily worked, 
and possesses great strength and durability. In the South the 
long-leaf yellow pine is found in abundance ; being harder and 
generally claimed to be stronger than the white pine, it is used 
for all purposes of construction, and can be obtained in long, 
straight sticks or logs, free from knots and many other defects. 
There exist two apparently distinct species, presenting practi- 
cally the same outside appearances. The one, however, has a 
large proportion of sap-wood and a small proportion of heart 
wood. This should not be used in structures unless immersed 
under water at all times. The other has very little sap, and 
long, large straight pieces can be obtained of almost clear heart. 
Such timber is unsurpassed for use in structures above ground, 
exposed to alternate wetness and dryness. In middle latitudes 
a pine grows, called commonly spruce pine ; is used freely 
where it grows, but is not considered equal to either of the 
above species in strength or durability. Nor is it in such 
abundance, but grows scattered over the ordinary forests in 
greater or less quantities, often high up on the sides of moun- 
tains, difficult to cut and haul, and is soon exhausted in any 
particular locality. 

36. For many years the pine trees of the South have 
been drained of their resinous matter yearly, called bleeding 
or turpentining. This is done by boxing the tree ; that is, cut- 
ting a bucket-shaped notch near the bottom, and a series of 
channels or grooves leading into it. The resinous matter drips 
into this bucket, and is removed at regular intervals. How 



I7§ A PRACTICAL TREATISE ON FOUNDATIONS. 

far and to what extent this affects the growth, ultimate hard- 
ness, strength, and durability of the timber, is not perhaps 
known. It would certainly seem to affect the tree injuriously 
in all of the above respects, and it is not uncommon to specify 
that no " bled " timber shall be used in trestles, bridge timbers, 
or other structure above ground. The owners of the forests 
stoutly maintain that it does not hurt or injure the timber, 
and the saw-mill owners generally side with them. Both are 
interested parties, as the one gets a double profit from the 
standing trees, and the second from the sawing. But whether 
it injures the timber or not is of but little practical value, as 
the " bleeding " is almost universal, and it is almost impos- 
sible to make large contracts under this restriction ; if you do, 
there is no means of detecting the difference between the 
two ; as a consequence, you may have to pay high for the 
requirement, and, after all, only get the bled timber. Some 
carpenters or experts say that they can distinguish the differ- 
ence. Some recent experiments have been made, and it has 
been reported that the bled timber is equal, if not superior, to 
the unbled ; but this can only be fully settled after years of 
experiment. 

37. Oak timber flourishes, apparently, in any country or 
section of the country, and possesses great hardness, and 
strength, as well as durability, but does not attain the same 
height ; is not as straight, is rarely free from knots of large 
sizes, and cannot be obtained in as long, straight pieces as the 
pines, but is largely used in many parts of the country. Its 
properties depend largely upon the nature of the soil in which 
it grows, that which grows in low or swampy lands being far 
inferior to that grown in the same latitude and same climate, 
but on the higher grounds. The first is soft and soppy, and has 
not the strength or durability of the second, and should not 
be used above the ground. Post oak, so called, seems to be a 
small white oak, but is considered even harder and stronger 
than the white oak ; but does not attain as great size, and is 
used principally for ties and other structures requiring small 
.cross-sections and lengths. Of the several kinds of oak, white, 



FRAMED TRESTLES. 1 79. 

red, black, post, and live oak, the white and post oaks are 
alone used in ordinary structures. The live-oak is the hardest, 
strongest, and most durable timber in the United States; is 
owned and reserved by the Government, and is only used in 
ship-building and other governmental structure. 

38. Cypress timber grows to a great extent in the Southern 
States ; is durable, and exceeds even the pines in this respect, 
as well as in the lengths and diameters of the trees. It has not 
the strength of the other timbers mentioned, but is often used 
for piles and for the various parts of the trestles, but in some- 
what larger dimensions when required to carry the same loads. 
Owing to the ease with which it splits into thin slabs, and its 
remarkable durability when exposed, it is used to a large ex- 
tent in making shingles, staves, weather-boarding, and the like. 
There is a species of this timber called black cypress, which 
has a durability equal to that of any timber. It is, however, 
rather scarce, and is rather small in diameter, but is much 
sought after for the piles of trestles in the Southern swamps. 
It is certainly far superior to the pines in durability. 

39. The writer does not mention the chestnut, poplar, elm, 
cedar, etc., as these are seldom found in such structures as are 
embraced in this work, though possessing many valuable and 
useful properties, and are largely used for many purposes re- 
quiring durability, ease of working, and where no great strength 
is required. 

40. There are a few general principles which will be of ser- 
vice in determining the general properties of the various species 
of timber trees. 

1. The heaviness generally indicates good timber, as does 
also the darkness in color. 2. The slowness of growth, as in- 
dicated by the narrowness and closeness of the annual rings. 
3. The larger the proportion of heart timber, which is gener- 
ally distinguished from the sap-wood by a darker color, and a 
harder, firmer material, the better the timber. 4. All timber 
grown on a sandy, elevated, well-drained area is superior to 
that grown on very low and swampy ground. 5. Of the same 
species, that grown in a cold climate is generally considered the 



l80 A PRACTICAL TREATISE ON FOUNDATIONS. 

best, whereas of different species the best is grown in a warm 
climate. But, fortunately, such timbers as grow in this 
country, whether North or South, and on almost any kind of 
soil, except a very swampy soil, that can be obtained in the 
requisite lengths and sizes for large, heavy structures, have 
the necessary strength, and are not materially different in 
point of durability. Our choice is largely controlled by 
circumstances. 



Article XXXVII. 

DURABILITY OF TLMBER. 

41. THE average life of timber when exposed will rarely ex- 
ceed from eight to ten years, and unless covered or preserved 
by artificial means of some kind, all structures should be entirely 
renewed in that time. The same timbers under apparently 
the same conditions are very variable in point of durability, — 
this may arise from one or more causes, which will be alluded 
to in another paragraph, — and a structure will begin to show de- 
cided evidence of decay in some of its parts in from two to four 
years. This can only be discovered by careful and continuous 
inspection. The renewal should therefore commence at an 
early day and be continued as the case demands until entirely 
renewed, anc, in fact, renewal and repairs should be practically 
continuous. It is due to the neglect to do this that many of 
our most serious accidents can be traced. The bulk of the 
timber used on railroads is consumed in building trestles, for 
both rapidity of construction and decrease of first cost often 
prove the impracticability of obtaining, on the first construc- 
tion of a road, a more durable material. Therefore on almost 
all new roads many very long and very high trestles are con- 
structed. These are called and regarded as temporary struct- 
ures, and are frequently not built with as much care and strength 
as they would be if intended to remain permanently as timber 
structures. Financial considerations prevent the substitution 
of earthen embankments, masonry arches or abutments, or 



FRAMED TRESTLES. l8l 

iron viaducts, — this is intended to be done from year to year, — 
and the old trestles must be maintained at a minimum cost for 
repairs. Rotten stringers and posts are patched up by spiking 
or bolting strips or planks to them, not unfrequently doing more 
harm than good. Heavier engines and trains are run over them, 
taking the risk, until finally the structure collapses, resulting in 
great loss of life or property ; and so-called experts are called in 
to explain the causes of the disaster. These often satisfy courts 
and juries, but, in fact, the structure has simply collapsed from 
inherent weakness on account of rot. 

42. Weakness resulting from rot generally arises at the 
joints, where timber rests on timber — as the surfaces of 
contact between tie and stringer, between stringer and cap, 
cap and post, post and sill. The deterioration does not take 
place first where it can be seen, but well in and under the top 
piece. The entire stringer may show a hard, firm, sound sur- 
face, yet in unseen parts it may be rotten to the core. 
(Simple knocking on the surface does not always indicate the 
exact condition of the interior. The writer has seen this tried 
many times, and erroneous reports made thereon. The only 
satisfactory test is to bore into the timber with a gimlet or 
auger, the bit not exceeding \ inch diameter.) It is easy to 
understand why this is the case. The moisture on an exposed 
surface evaporates rapidly under the influence of the sun and 
wind, whereas that portion which lodges in the joints between 
the timbers remains for a longer time, and if it has access to 
the ends of the timber it will spread for a considerable distance 
in the direction of the length of the stick. The moisture and 
internal heat combined with all the conditions favorable to 
decay, rot will take place in the interior of the stick and 
under the top stick. This is the condition with the ends of 
the stringer, the top and bottom of the posts, and to a less 
degree under the ties. Stringers may be perfectly sound in 
the middle of their lengths, and rotted to a dangerous degree 
at the ends, especially on the under side. The same in the 
posts. The writer has examined miles upon miles of old 
trestles, boring into the timbers at the ends and at one or two 



1 82 A PRACTICAL TREATISE ON FOUNDATIONS. 

intermediate points, and rarely has he observed any variation) 
from the above rule. The mortise-and-tenon joint, is partic- 
ularly favorable to bring about the above injurious conditions. 
This will be further alluded to in discussing the subject of 
joints. On examining an old structure, bore into the ends of 
the stringers, the top and bottom of the posts, and obliquely 
under the ties at the middle of the stringer. If no signs of 
decay are thus discovered you may be satisfied that the rest 
of the piece is sound, unseen defects existed in the begin- 
ning, which generally should be seen on the outside ; and this 
timber should have been originally condemned. Oak timber 
sometimes, when standing, is rotten in the centre, but this will 
generally be discovered in cutting down the tree, or in the 
subsequent sawing of the log. 

Article XXXVIII. 
MEANS OF PRESERVING TIMBER. 

43. TIMBER should be free from such defects as cracks 
radiating from the centre, or cracks which separate one annual 
layer from another, splitting as it were into rings, or upsets 
where the fibres have been injured by compression, or large 
knots. Doty or spongy places indicate incipient decay. 
Almost all timber will show cracks when exposed, after being 
cut, in the green state, to the sun or high winds. If these only 
extend to a short distance into the timber, and for short dis- 
tances in the direction of its length, no especial notice need be 
taken of them, for the cracks are, in fact, unavoidable ; but if 
they extend half the way or all of the way through a stick, it 
should be condemned, as they materially weaken the timber, 
and in addition will aid in hastening rot. Large knots also 
weaken the timber, as they do not adhere strongly to the sur- 
rounding fibres, and in addition the fibres themselves around 
the knots are upset or crippled. The knots also in time fre- 
quently become loose and separate from the surrounding 
timber. A limited number of small knots, if not occurring in 



MEANS OF PRESERVING TIMHEK. 1 83 

the same vertical or horizontal plane, or not extending entirely 
through the stick, need not be a serious objection. A little 
sap on the corners of large sticks has practically the effect of 
reducing the area in proportion to the amount of sap, as the 
sap rapidly rots. It is almost impossible to secure large-sized 
timbers in great quantities entirely free from all of the above 
defects, but the right to limit the defects should be reserved 
by the engineer. This is done by specifying that the timber 
shall be clear-heart, and free from any of the above defects. 
The material must be either condemned at the mills or on de- 
livery at the site of the work. 

44. The best method of preserving timber is by natural 
seasoning; this is done by exposing the timber to air in a dry 
place, but protected from hot suns or high winds. This is a slow 
process and requires many years ; the time may be lessened 
by first soaking the timber in water, as this will dissolve a por- 
tion of the sap, and the drying will be more rapid. In artificial 
seasoning the timber is exposed in a close building to a current 
of hot air, the time required depending upon the dimensions 
of the timber. In both cases the timber should be piled 
with such intervals as will allow free contact of the air with its 
entire surface, the object of all seasoning being to extract the 
sap from the pores of the timber. The immense demand for 
timber has practically rendered natural seasoning impossible, 
and nearly all timber used in floors, doors, window-frames, 
mouldings of houses, etc., is artificially seasoned. But for the 
large structures on railroads, and similar structures, the timber 
has little or no seasoning, and where great durability is required, 
some artificial method of preserving the timber must be re- 
sorted to. But it is useless to resort to any of these means 
unless the sap is first removed, as the object of seasoning is to 
remove the sap, so the mode of preserving the timber is to 
keep the moisture from again entering the pores, by filling; 
them either entirely or partly at and near the exposed surfaces 
with a durable and impervious substance. 

45. For wooden bridges a very excellent method is to en- 
tirely enclose the bridge in a sheeting of plank and a tin or 



184 A PRACTICAL TREATISE ON FOUNDATIONS. 

shingle roof ; by this means the timber has time to be naturally 
seasoned at the same time that the structure is being used. The 
timber in such cases will last for many years ; cracks will be 
prevented, and if at the expiration of one or two years the 
timbers of the bridge are painted and kept well covered with 
paint, the structure will last for a great length of time. But the 
practice of painting timber before the sap is entirely removed 
is to be condemned, as it does more harm than good ; it pre- 
serves the timber from decay on the surface, but hastens the 
rot on the inside. Builders of wooden bridges are always in a 
hurry to paint the timbers, as it tends to prevent cracks before 
the structure is completed ; but cracks are the lesser evil of the 
two. Timbers of bridges should not be painted when fresh from 
the mills. The red paints are almost exclusively used ; but 
these differ materially in durability, and only the standard 
brands should be used. Oil paints in any colors can now be 
purchased in cans or barrels, and ready-mixed for use. A coat- 
ing of pitch or tar is also used as a paint ; it is unsightly, but 
gives good results. 

46. Other artificial means of preserving timber consist in 
filling the pores of the timber with solutions of metallic salts, 
such as copperas or sulphate of iron, corrosive sublimate or 
bichloride of mercury, chloride of zinc, sulphate of copper. 
The timber can be saturated with these salts after the sap has 
been expelled, or forcing them into the pores under pressure, 
driving the sap ahead. All of these substances seem to pre- 
serve the timber as long as they remain in the pores ; but they 
are gradually dissolved and removed by water. Owing to the 
^expense and time required in the application of these they are 
but little used in this country. Owing to the abundance and 
^cheapness of good timber, it is found more economical to let 
the timber rot and renew the structure from time to time. 
Creosote, or the heavy oil of tar, has, however, been used to 
a considerable extent in this country, and it is claimed that, 
although it will materially increase the first cost of the struc- 
ture, it will ultimately prove economical, as it adds greatly to 
the durability of the timber, which lasts three or four times as 



MEANS OF PRESERVING TIMBER. 1 85 

long as timber not creosoted. The sap and moisture are first 
exhausted by creating a partial vacuum in an air-tight vessel or 
tank, and then forcing the creosote into the pores of the timber 
under a heavy pressure. This is a rather expensive process, 
making the cost of the structure from 2 to 2.\ times as much 
as the natural timber, and for the reason above stated it is used 
to only a limited extent. If it were universally used, the cost 
might be materially reduced. As it is, the application is mainly 
■confined to the treatment of piles and timber used in sea-water; 
here it becomes a necessity, as timber is rapidly destroyed by 
sea-worms. The Teredo navalis enters the timber no larger 
than the point of a pin, and eats towards the centre, growing 
.as it progresses, reaching the size of a grub-worm. Thousands 
of these worms attack the timber, completely honeycombing 
it, and destroying it in less than a year. It is difficult to detect 
the infinitesimal holes on the surface. Large piles have to be 
renewed in a year after immersion. These worms, however, 
only eat between the low-water line and the bed of the stream. 
It has, therefore, been suggested to cover the piles with a 
sheeting of copper or copper tacks, or to fasten a hollow cast- 
iron cylinder to the top of the pile, and drive the pile by means 
of blocks of wood resting on top of the iron, to receive the 
blow of the hammer, or to place a follower, a short pile in the 
cylinder, resting on top of the pile, and reaching above the cyl- 
inder in order to transmit the effect of the blow. Iron, however, 
stands but poorly the corrosive effect of sea-water ; none of 
these have yet been proved to give economical and satisfactory 
results. Creosote is, therefore, commonly resorted to.* 

47. The durability of timber is materially affected by the 
time of cutting down the trees ; this should be done generally 
in the winter, when the sap is not running. Ordinarily, little 
attention is paid to this, and the trees are cut down and carried 
to the mill when needed, regardless of the time of the year. 

* So-called " vulcanized timber " is now produced by subjecting green 
timber to a great pressure and high temperature, which converts the sap and 
other deleterious fluids into antiseptic compounds, which become more or less 
solid and impervious to water. Experiments indicate an increased strength, 
stiffness and durability. 



l86 A PRACTICAL TREATISE ON FOUNDATIONS. 

The age at which trees are cut is also a matter of much impor- 
tance. Owners of forests desire to get rid of the older trees,, 
and timber from trees that show evident signs of deterioration 
from age is often forced on the engineer. Such timber is brittle,, 
sometimes soft, spongy and " doty "; the latter can be easily 
detected by its appearance, and it will clog the saw while cutting 
through it ; such timber has really commenced to decay, and 
will rapidly rot when exposed. Often a stick of timber will 
show this "dotiness" at one end ; the other end may be per- 
fectly sound, apparently, and even cutting off a foot or two, the 
entire stick may seem sound and have a better appearance 
than many other pieces It is hard to condemn such timber, 
and it is often, if not generally used. It is a safe rule, however,. 
to condemn, as it evidently indicates a defective tree. 

48. All kinds of timber constantly immersed in water will 
last indefinitely. Timber exposed to alternate moisture and 
dryness will decay rapidly, as also when moist, and in a warm 
or confined air. Timber exposed to confined air alone decays. 
by what is known as " dry rot," and crumbles into a powder. 

49. As before mentioned, in exposed structures, such as- 
trestles, the timber rots first at certain well-determined points, 
as the joints in framed structures, and while it is expen- 
sive and impracticable to undertake to preserve the timber of 
such structures by any of the processes above mentioned, it is 
easy and comparatively inexpensive to prolong the life of these 
timbers at the joints, and thereby the life of the entire struc- 
ture, as the strength and durability of the weakest part 
measures that of the whole structure. This is done simply by 
painting all surfaces of contact between timbers, as the top and 
bottom of every post, the ends of the stringers, with hot asphalt 
or coal-tar, either alone or properly thickened with lime, applied 
just before putting the parts together; this is simple, cheap, 
easily and rapidly applied. To include this item in the contract 
would cause an exaggerated demand for increase in price. It 
would be carelessly executed and often neglected altogether ; 
but even under these circumstances it would be a great im- 
provement on the ordinary plan. But it would pay the com- 



MEANS OF PRESERVING TIMBER. 187 

pany to employ a man whose entire time should be devoted to' 
a faithful discharge of this duty, and to purchase the necessary 
materials. Three fourths of the timber removed from old 
structures is often as sound as when first used ; and, if this 
simple remedy will preserve the remaining one fourth, it should 
certainly be adopted. 

Article XXXIX. 

TIMBER TRESTLES— (CONTINUED). 

50. THERE are two other types of trestle possessing several 
advantages, but seem to be seldom used ; these will be briefly 
described. In the first, whether the trestle is one or more 
stories high, the posts are made of several small pieces of 
timber bolted together, instead of one piece, as in the ordinary 
trestle. Four pieces, 6 ins. X 6 ins., give an area of 144 square 
inches, the same as one piece 12 ins. X 12 ins. These pieces 
bolted together with packing blocks between give stiffness to 
the columns by increasing the ratio of the least diameter to 
length ; cross and longitudinal pieces can be placed between 
the pieces, making thereby in some respects a better and 
stronger connection between all of the main members of the 
structure, and with an increased number of bolts ; pieces and 
members can be built into a structure possessing great stiffness 
and strength. This form of trestle has been used in very high 
trestles and timber piers. The columns may contain any 
number of the small pieces bolted together, depending upon the 
height of the trestles and the length of spans to be carried. 

51. The other type differs slightly from any of those above 
described. The writer has never seen it constructed, but it 
seems to possess the advantage of bringing each member to bear 
a part of the load at the same time that it gives spread to the 
base and increased lateral stiffness ; it can be better understood 
by conceiving each story first, as framed for a single story 
trestle ; set one on the top of the other, and each successive 
story to have one additional batter-post on each side of the 
centre parallel to the batter-post in that section, but placed so 



1 88 A PRACTICAL TREATISE ON FOUNDATIONS. 

as to be in the prolongation of the batter-posts in the sections 
above ; the caps and sills of each section being lengthened to 
suit the above conditions, the usual longitudinal and diago- 
nal braces being used. In this construction, the outside 
batter-posts extend in one continuous line from top to bottom, 
the next from the bottom of the first to the bottom, and so on. 
This avoids a sort of haphazard placing of the additional 
pieces in the lower sections, which often exists, and some- 
times looks as if pieces of timber were simply inserted to fill 
up vacant spaces, without any regard to their forming any in- 
tegral part of the structure itself. And in fact, the strength of 
the timbers exceed so many times the strains brought upon 
them that not much pains is expended upon placing them in 
such a manner as to be of any great advantage. (See Figs. I, 
2, 3, and 4, Plate VII.) 

52. In trestles especially, the joints are of importance, as 
the structure is generally built of green timber entirely; is 
exposed to all conditions of weather without any protection of 
any kind, and is generally run over at high speed, causing . 
constant hammering and vibration, if at all loose. The repairs 
are made in detail and constantly, without stopping the trains. 
One piece is taken out at a time and a new piece inserted. 
Some forms of joints are more liable to rot than others ; some 
reduce the effective bearing surfaces more than others ; some 
make it more difficult to remove a piece than others. There- 
fore that form of joint which offers the least number of the 
above objections, due regard being had to the strength of the 
structure, should be adopted. 

Article XL. 
JOINTS AND FASTENINGS. 

53. The principal joint in trestles connects a strut and a tie 
or a strut and a beam. As a general rule, the mortise-and-tenon 
joint is used. (See Figs. 1, 5, Plate VIII.) This joint is formed 
by cutting a rectangular hole in the face of one of the timbers, 
about 8 or 8£ ins. long, 3 to 3^ ins. broad, and about 6 ins. 



JOINTS AND FASTENINGS. 1 89 

deep, and cutting on the end of the other piece a tenon, theo- 
retically of the above dimensions, but practically from \ to -|- in. 
smaller in each dimension. This tenon is inserted into the mor- 
tise, and in a hole from \\ to \\ ins. bored through the tenon 
an oak pin or treenail is driven ; this constitutes the connec- 
tion. In this joint from 24 to 27 sq. ins. of bearing surface are 
lost at the centre of the post, as the tenon never fills accurately 
and fully the mortise. The bearing surface of the post con- 
sists in a narrow shoulder around the tenon. Not unfrequently 
the post has sap on the corners, extending often on the face of 
timber for several inches, practically reducing the bearing sur- 
face in proportion to the amount of sap. The mortise forms a 
receptacle for water ; sometimes a hole is bored in the bottom 
of the mortise entirely through the timber. This prevents any 
great accumulation of water, and affords also slight ventilation ; 
but nevertheless water enters, and remains for a greater or less 
time. The tenon only serves to hold the pieces together. 
This joint, therefore, reduces the strength of the pieces, in- 
creases the tendency and rapidity of decay, the strength of 
the joint itself depending upon a small projection of timber in 
conditions most favorable for rot. Yet it is used more than 
any other joint. The hot tar and lime paint would certainly be 
of very great advantage in this case. It is difficult to insert a 
new timber, when a rotten one is removed, without lifting the 
entire cap. The cost of framing is somewhat increased in 
cutting the mortise-and-tenon. 

54. The writer has for the above reasons used to a great 
extent the joint shown in Fig. 2, Plate VIII. This joint is 
formed by simply cutting a notch or dap about 1 in. deep entirely 
across one of the pieces ; the end of the other is simply cut 
square, fitting into the dap. By this means the entire strength 
of both pieces is available, moisture is less apt to enter and 
remain, a new piece is more readily inserted. The rotting of 
the sap on the outside of the timber affects the strength of the 
post but little in proportion, as the harder and stronger heart 
remains. The post can be slightly chamfered at the top, so 
that the cap can slightly project over it, materially aiding in 



iC)0 A PRACTICAL TREATISE ON FOUNDATIONS. 

excluding the water. The pieces are held together either by 
drift-bolts, or preferably by straps and bolts, drift-bolts render- 
ing repairs very difficult. Timber strips can be used instead 
of iron straps, but this increases the tendency to rot, and makes 
a bungling-looking joint. It would seem that this joint would 
possess in every respect a great advantage over the mortise- 
and-tenon joint. 

55. A dovetail-joint, or a joint formed by halving the tim- 
bers into each other, as in Fig. 3, Plate VIII, and bolted to- 
gether, forms a good connection, but is rarely used in trestle 
construction ; yet it is the usual joint used where both of the 
pieces are horizontal, particularly in cribs for holding concrete 
or broken stone, and in the walls of crib coffer-dams, as the 
pieces act both as a strut and tie brace. 

56. The caps and sills are sometimes made in two pieces 
6 ins. X I 2 ins., instead of one piece 12 ins. X 12 ins.; these 
pieces placed an inch or an inch and a half apart ; daps of suf- 
ficient depth cut into these, so that the tenon can enter between 
them ; the pieces bolted together between the posts and also 
through the tenon. This possesses the following advantages : 
The tenon has good ventilation and does not rot so rapidly; 
the cap and sill are likewise preserved ; new caps, sills, and 
posts can be inserted with ease. 

57. The inclined or batter posts of trestles are connected 
in the same manner as the vertical post. When the mortise- 
and-tenon joint is used, it is so cut that the tenon stands in a 
vertical direction when connected, and not in the prolongation 
•of the axis of the piece, as seen in Fig. 5, Plate VIII; or it 
can be made as seen in Fig. 6, Plate VIII. In these cases the 
tenon or shoulder should be at least 2 ft. from the end of the 
piece in the direction of the strain, so as to prevent shearing off 
the timber. If the posts are very much inclined, this tendency 
should be resisted by bolts as shown in Figs. 6 and 8, Plate 
VIII. This is rarely ever necessary or used in trestle construc- 
tion. 

58. Longitudinal bracing is not generally used in a single- 
story trestle, unless the trestle is quite high ; but is always used 



JOINTS AND FASTENINGS. IC)I 

In a trestle of two or more stories. It is a good and safe rule, 
however, to use it whenever the trestle is over 10 or 12 ft. high. 
A continuous course of 3-in. plank, spiked or bolted to the out- 
side posts, will add greatly to the stiffness of the trestle, ar.d 
should always be used if the trestle is constructed on a grade 
or incline. If spiked to the top of one bent and the bottom of 
the next in the direction of the descending grade, it will be 
more effective than if placed horizontally. For higher trestles 
it is 6 X 6 in. or 8 in. timber, and is bolted to all posts, at the 
top of each section. Diagonal longitudinal bracing is also 
sometimes used. The horizontal bracing at the division be- 
tween the sections or stories is generally notched over the 
caps as well as bolted to them. 

59. Besides the above-mentioned joints, which are principally 
used in connecting pieces that make either acute or right 
angles with each other, there are others for lengthening ties or 
struts. In the case of struts which transmit a compressive 
strain, all that is necessary for this purpose is to bring the ends 
square together. But unless fastened in position, there is dan- 
ger of one piece slipping on the other. This can be prevented 
by the simple fish-joint, which consists in spiking or bolting 
strips of wood or iron straps to the faces of the pieces (see 
Figs. 12, 13, and 14), or by halving the pieces together and hold- 
ing them in position by bolts or straps, or by a combination of 
these (see Figs. 10 and 14, Plate VIII). When the pieces overlap 
and are bolted together the joint is called a scarf joint. Any 
of these joints shown in the above-mentioned drawings will 
serve to lengthen struts. But as the strain on the bolts, straps, 
or fish-plates is small, the simplest connection is the best and 
the cheapest. Iron sockets are used also in many cases, the ends 
of the pieces being simply inserted into the open space, and may 
or may not be bolted ; or holes may be bored into the ends 
of the pieces, and an iron pin inserted in one piece and pro- 
jecting out, the other piece being then placed on top. This 
makes a rather weak connection if there is any tendency to 
bend. Round timbers, such as piles, can be lengthened by 
halving the pieces, and when placed together drive iron rings 



I9 2 A PRACTICAL TREATISE ON FOUNDATIONS. 

on tightly so as to bind or clasp the pieces together. This is 
perhaps the best method of splicing piles. 

60. To join ties together, any of the joints (Figs. 10, II, 12, 
13, and 14, Plate VIII) answers the purpose ; that is, either the 
fish or scarf joint, or both. It must be remembered in this 
joint that as the tendency is to pull the pieces apart, the con- 
nections or fastenings have the entire strain to bear, and should 
therefore be as strong as the parts connected, after deducting 
for bolt-holes, indents, etc. We will describe each joint briefly. 
Fig. 12 is a simple fish-joint. The aggregate strength of the fish- 
plates A must be the same as that of the uncut pieces ; their 
length must be such that when under maximum tension the 
bolts must not shear or cut out to the ends of either the fish- 
plates or the main members ; or the area sheared or split, multi- 
plied by the resistance to shearing must, be equal to the area of 
the ties multiplied by the resistance to tearing, also to the sum 
of the areas of all the bolts multiplied by the resistance of 
wrought-iron to shearing across ; or in symbols, F X s =T X t 
= B X h in which F = equal area of timber liable to shearing, 
s = safe resistance to shearing per unit of area; T= to effec- 
tive cross-section of ties, i.e., after deducting bolt-holes, indents, 
etc. ; / = safe tensile strength per unit of area ; B = sum 
of areas of bolts; i = resistance to shearing of iron per unit of 
area. Assuming unit of area as 1 sq. in., and area of ties as 
144 sq. ins. (12 X 12 in. sticks), and substituting the average 
units of strength, we have F X 400 = 144 X 1000 = B X 40,000, 
hence F= 360 sq. ins., or in a stick 12 ins. deep a single bolt 
should be at least 2.5 ft. from the end of the timbers, or two 
bolts in the same distance, one 1.25 ft. from the end; and 
B = 3.6 sq. in., or two bolts 1^ in. diameter. This gives the 
least allowable values for F and B, as the least unit values for 
tensile strength and the greatest unit values for shearing, both 
for iron and timber, is used. In this case both fish-plates and 
bolts have the entire strain to bear, each on its own account. 

61. In Fig. 13 the fish-plates are indented into the ties; the 
effective area of the tie is therefore reduced to that extent, and 
the strength of the connections is increased as additional areas 



JOINTS AND FASTENINGS. I93 

are presented to resist shearing ; therefore the connections need 
not be as strong as in the first case. The principle of determin- 
ing the number of the bolts and their position, as also area of 
fish-plate to be sheared, are the same as above. But this joint 
sacrifices the strength of the main tie, and causes great waste 
of material. Both joints present a bungling appearance. Iron 
bars or straps answer the same purpose and look much better, 
and in permanent structures are ultimately more economical. 

^ 62. In the simple scarf-joint, Fig. 10, the strength of the 
joint depends entirely upon the resistance to shearing of the 
timber and the iron bolts ; the effective area of the tie is re- 
duced to one half; consequently 50 per cent of the timber is 
wasted, in addition to the waste in the overlap, each stick 
being from 4 to 8 ft. longer than actually required in the fish- 
joint. In these joints hardwood keys are introduced, as shown 
in the drawings ; these being driven between the ties, project- 
ing an inch or two into both, increase the areas to be sheared, 
the bolts serving mainly to bring the parts into close con- 
tact. Fig. 14 shows a combination scarf and iron fish-joint, 
with bolts and keys. It does not seem to possess any advan- 
tage over the plain fish-joint with iron straps, and is more 
difficult to frame. Keys should always be placed horizontally ; 
if vertical, water easily enters, and causes rot. Fig. 1 1 shows a 
scarf-joint which will hold without bolts ; only one third of the 
strength of the timber is secured, and unless the timber is 
thoroughly seasoned, and the framing carefully executed, there 
is but little strength in the joint ; bolts should always be used 
in all joints to resist a tensile strain, whether fish or scarf 
joints. 

63. Timber has a greater resistance to tearing than it has 
to crushing, but owing to the difficulty of connecting several 
pieces to resist tensile strain, as seen above, without great waste 
of material, the general practice is to use timber for members 
under compressive strain and iron for those members under 
tensile strain, unless single sticks can be secured of sufficient 
length. In Howe-truss bridges for railways, and timber high- 
way bridges, the bottom chords are made of timber. In the 



194 A PRACTICAL TREATISE ON FOUNDATIONS. 

first iron fish-bars are almost always used at the joints, in the 
second wooden fish-plates with indents or projections: and 
in addition the chords are made of three or more pieces thor- 
oughly bolted together at short intervals, with iron or wooden 
packing-blocks between. 

64. Figs. 8 and 9, Plate VIII, show the construction of king 
and queen post roof or bridge trusses for spans from 20 to 40 ft. 
in length. The lower horizontal member is called the tie-beam 
and is under tension ; the upper is the straining beam and is 
under compression. The end inclined members are struts under 
compression. The verticals are ties under tensile strain ; the one 
on the left is a single piece resting on top of the tie-beam and 
connected with it by a stirrup, which is simply an iron strap, or 
"bar bent at right angles at the ends, passed up under the tie- 
beam and held by bolts to the vertical. The one on the right is 
made in two pieces, the tie-beam passing between them and 
resting on shoulders cut in them from 1 to 2 ft. from the lower 
end, the two pieces held together by bolts, packing-blocks 
being placed between where necessary. This is an over- 
trussed or through span. Fig. 3, Plate VII, represents the 
under-trussed or deck span constructed for the same purpose. 
This is used in trestle-work when the spans are from 20 to 25 
ft. from bent to bent. Instead of these trussed beams, timber 
built beams are sometimes used. Figs. la, 2a, 4a, $a, 6a, 
Plate VIII, show this construction, in which 2, 3, or 4 pieces 
of timber are built together with bolts and keys. Two pieces 
12 X 12 ins., one on the top of the other, will answer for spans 
from 12 to 15 ft. long; two pieces side by side, with a 
third on top, for spans from 15 to 20 ft; and four pieces 
for spans from 20 to 25 feet.. It is evident that there is a 
great waste of timber, and it is badly distributed to meet the 
required conditions of strain. Single pieces properly trussed 
would be more sightly and more economical. Beams are built 
also, either as straight or curved beams, of plank laid flatwise 
and bolted or spiked together, and are frequently used in 
bridges and roofs ; their strength is materially less than a solid 
.beam of the same cross-section, probably not more than from 



JOINTS AND FASTENINGS. IQ5 

one third to two thirds as strong. As a rule, they would not 
be used when large sticks could be secured, except in tempo- 
rary structures, such as centres for arches (Figs, ja, 8a, ga, 
Plate VIII). From the above description, there are certain 
general principles applicable in constructing all joints. 

i. The joints should be so cut, and the fastenings so pro- 
portioned and placed, as to weaken the main members as little 
as possible. 

2. The strength of the fastenings, bolts, straps, and fish- 
plates, either singly or together, should be equal to the effective 
strength of the parts connected, and their areas should be 
inversely proportional to their unit strength. 

3. All surfaces in contact should fit exactly throughout, and 
the direction of the planes of such surfaces should be perpen- 
dicular to the direction of strains, and their areas should be suffi- 
ciently large to keep the unit strain of that particular kind within 
loads safe limits, allowing a factor of safety of 4 in case of 
steady and of 10 in case of moving loads. 

4. All joints should be so arranged and placed as to pre- 
clude, as far as possible, access to water, and should be painted 
with some substance impervious to water. 

5. The joints will in general be the weakest part of the 
structure, and should be taken as the measure of the strength 
of the whole. 

6. In all built or packed beams the parts composing the 
beam should break joints as far as possible. 

7. Where joints are formed by indents, shoulders, or tenons, 
and held together by bolts or straps, each should have suffi- 
cient strength to transmit the entire strain, as from shrinking 
of timber, loosening of bolts, or other causes, either may have 
to bear the entire strain. This is applicable in all cases, except 
in lengthening struts, unless constant inspection is made to 
see that all parts are properly adjusted. 

8. Although there is always a consideration, admissible, 
of the frictional resistances between surfaces in contact, this 
should not be relied upon to any but a very limited extent, if 
at all. 



ICp A PRACTICAL TREATISE ON FOUNDATIONS. 

Article XLI. 

SUPPORTS FOR TRESTLES. 

65. Trestles are supported in three ways: 1. By mud-sills ; 
2. By masonry pedestals ; 3. By piles. 

If any pretext can be offered the first is always adopted ; they 
consist of from 4 to 6 pieces of timber, of any size convenient, 
generally 4 or 5 ft. long, placed under the bottom sill, either 
wholly or partly imbedded in the ground, shallow trenches be- 
ing excavated to receive them. With no precautions taken to 
provide drainage, and regardless of the nature of the soil, nat- 
urally water collects in the trenches, converts the soil into mud, 
the motion of the train produces a churning action, the trestle 
rises and falls, gets out of line and level, is then adjusted by 
driving shingles, thin strips of plank, or anything that can be 
procured under the sills, and this is repeated until these strips or 
shims are piled one on the top of the other for 6 or 8 ins. or more, 
sometimes only under one or two of the posts. Under such 
circumstances the wonder is that accidents are not many times 
more frequent than they are. Occasionally engineers require a 
double row of sills to be laid first and the mud-sills placed across 
and at right angles to these. This serves several purposes : it 
may place the foundation-bed below the injurious action of 
frost ; it increases the area of bearing surface ; it lifts the sill 
slightly above ground, permitting ventilation and consequently 
preserving the timber ; it is certainly not very expensive. It 
should always be required. 

2. When the nature of the ground will admit of mud-sill 
under trestles, it will generally be found that rubble-stone can 
be obtained at a small cost. Small rubble pedestals should 
then be built, in pits from 1^ to 2 ft. deep and extending from 
6 ins. to 1 ft. above ground. A single pedestal 2 to 2-| ft. square 
under each post will be sufficient. This is as much superior to 
the last method as that is to the simple mud-sill. 

3. Piles are used when the ground is very soft for any great 



JOINTS AND FASTENINGS. 1 97 

depth below the surface, or in swamps. These can be cut off 
below the moisture line or above the surface. One pile is driven 
so as to be under each post of the trestle ; the sill rests on the 
piles, and is fastened to them by mortise and tenon, by drift- 
bolts, or by straps. Commonly where piles are necessary, the 
trestles are comparatively of small height, the piles reach well 
above ground, and the stringers rest directly upon them. In 
such cases the structure becomes distinctively a pile trestle, as 
distinguished from a framed trestle, and will be explained 
under that head. 

66. Framed trestles may be divided into four classes or 
types presenting some marked differences in construction. 

1. That in which the principal members are vertical, except 
the outside batter-posts, inclined braces of smaller cross-section 
being introduced to give steadiness and stiffness. This is 
probably more generally used than any other. Fig. 3, Plate VI, 
represents a single story or section. 

2. The M trestle, in which all of the main members are 
inclined, and verticals introduced only in the very high trestles, 
auxiliary inclined braces of smaller cross-section being also used. 
See Fig. 4, Plate VI, for single story, and Figs. 1, 2, Plate IX, 
for two or more stories, with details of important parts. 

3. The trestle in which the columns are built up of pieces 
of small cross-section, instead of single pieces of larger cross- 
section. It can be put together as in either of the above 
types. 

4. That form in which two vertical columns extend from 
top to bottom, inclined members are used to bear a portion 
■of the load, and to act as main members and braces at the same 
time. See Figs. 1, 2, 3, 4, Plate VII. This form of trestle has 
never been used to the writer's knowledge, but it certainly 
seems to be as strong as, if not stronger than, the other trestles 
in common use. It will be noticed that straps are used, instead 
of the mortise-and-tenon joints. The writer believes that 
they make a better and stronger trestle. It is also shown 
as resting on masonry pedestals for the same reason. 
Either of the above forms of trestle is strong enough, and 



I98 A PRACTICAL TREATISE ON FOUNDATIONS. 

that one should be adopted which requires the least material, 
requires the least amount of work in framing and erecting, and 
is more easily renewed and repaired in whole or in part. 
Fig. 2, Plate VII, shows the method of trussing the stringers by 
the use of straining pieces and struts, and Fig. 3 by the use of 
iron rods. In the latter case it is better to use two ties or rods,, 
and, to prevent the necessity of boring holes in the string-pieces, 
the stringer should be made of three pieces, with small inter- 
vals between them through which the rods can pass. On the 
ends of the stringers thick iron washers should be placed,, 
through which the rods pass and upon which the nuts bear, so> 
as to prevent the rods from cutting into or crushing the fibres 
of the timber at the ends of the stringers. As the spaces are 25 
feet from bent to bent, the stringers do not break joint on the 
cap, and unless bolsters or fish-plates are used, the stringers, 
would not have over 5 inches of bearing on the caps, which is 
not enough. In Fig. 2, Plate VII, two 6-inch fish-plates are 
bolted to the stringers and rest on the cap ; by this means 
the bearing surface is increased and at the same time the 
stringers are tied together. This the writer prefers to the: 
bolster connection as shown in Fig. 3 under the stringer and. 
bolted to the cap. 

67. All of the main members of the trestle-bent are sub- 
jected to a compressive or crushing strain, except the bottom 
and intermediate horizontal pieces or sills ; these are subjected 
to a tensile strain and a crushing strain across the grain by the 
pressure on the posts. The tensile strain tends to shear the 
layer of timber between lower end of each post and the end of 
the sill. To resist this the end of the post should be from i|- to 
2 ft. from the end of the sill, as shown in all of the drawings. 
As the inclination of the batter posts is small, this strain is 
small, and consequently bolts are not needed or used. The 
strength of the timber to crushing transversely, whether pine 
or oak, is very great ; the greatest loads that can possibly 
come on the posts would make no impression on the timber of 
the sills between them. Trautwine says that a pressure of 
1000 lbs. per square inch will not indent yellow pine or oak 



JOINTS AND FASTENINGS. 1 99 

more than the thickness of a sheet of writing paper, and white 
pirte not over \ of an inch. The writer has subjected soft 
pine cushions in testing the crushing strength of stone, to a 
pressure of 5000 lbs. per square inch, with no perceptible effect 
upon them. The upper cap is under both longitudinal and 
transverse crushing strain, and always has ample strength. 
The posts are under longitudinal compression. The lengths of 
such pieces in proportion to their least dimension is an impor- 
tant factor in their strength. In very short columns the resist- 
ance to crushing is simply proportional to the area of the cross- 
section. 

68. The coefficient of resistance to crushing, or the strength 
per square inch of area, for green timber is about 5000 lbs. per 
square inch. This, however, decreases in a rapid ratio as the 
length increases, and when the length is 30 times the diameter 
or least side it would crush under less than \ of 5000 = 250a 
lbs. per square inch, and the safe load should not exceed \ to 
y 1 ^ of this, or from 500 to 250 lbs. Seasoned timber is about 
twice as strong as the green timber. The usual practice is that 
the length of the column should not exceed 20 times its least 
dimension, or a stick 12X12 ins. should not be more than 20 
ft. long ; so we find that the height of a story or section of a 
trestle-bent does not exceed 20 to 25 ft. If the bents are \2\ ft. 
apart, the greatest load per foot of span would be about 6000 
lbs. or 75,000 lbs. on each bent of the trestle. This is really sup- 
ported by four pieces, but two pieces 12 X 12 in. = 144 square 
inches would bear safely, at the low limit of 250 lbs. per square 
inch, 72,000 lbs. ; but assume that the two batter posts together 
bear \ of the load and the two vertical posts § of the load',. 
each vertical post would carry only 25,000 lbs., and each batter 
post 12,500 lbs. A X 250= 25,000, and A' X 250= 12,500; or 
the area of the vertical posts = A = 100 sq. in.; or one piece 10 
X 10 ins. or 12 X 8£ ins. would be sufficiently large for the verti- 
cal posts, and for the batter posts A' = 50 sq. ins. or 1 piece 
6% X 8 ins., and in the M trestle each post would carry ^ 

X 75,000 = 18,750 lbs. A = — 15- =x 75 S q. ins. and each post 

250 



200 A PRACTICAL TREATISE ON FOUNDATIONS. 

would be 8 X 9i or 8| X 8f ins.; but in either case the dimen- 
sions are seldom if ever less than 10 X 12 ins., and more com- 
monly 12 X 12 ins. in cross-section. 

69. In the case of a 25-ft. span the uniform load per foot 
of length would not exceed 5000 lbs., or on each bent 125,000. 
In the M trestle each post would carry 3 1,250 lbs. its area need 
not exceed 125 square inches or one piece 12 X io| ins.; and for 
other forms of trestle, assuming as before one third of the entire 
load as borne by the batter-posts and two thirds by the vertical 
posts, the batter-posts would be 10 X 9 ins. each and the verticals 
12 X 14 ins. In this calculation the column or post is supposed 
to be at least 30 ft. long, which is rarely the case, the diag- 
onal or X bracing increases its strength materially; so it will be 
seen that even in 25-ft. spans the verticals need not exceed 12 X 
12 ins. In very high trestles the pressure on the lower posts 
is increased by the weight of the structure; but as the number 
of posts is greater in the lower sections, the unit pressure on 
any one post would never exceed that of the posts in the 
upper story, and no increase in the area of the posts is neces- 
sary in the lower sections above the dimensions given above 
and shown in the drawings, though the bottom posts are 
sometimes 12 X 14 ins. 

70. To determine the area of the cross-section of the 
stringers we will use the formula mWl= nfbH\ as the beam 
is under a transverse load of 6000 lbs. per lineal foot, and is 
liable to give way by bending or cross-breaking. The greatest 
possible load is 6000 lbs. per foot, and the unsupported length 
of span, being in bents \2\ ft. centres, only \\\ ft. The total 
uniform load is 69,000 lbs., and the equivalent centre load 

— "9'° 9 — 34,500 lbs.; and as this is supported by four pieces 

2 
6 in. wide or thick each, each piece will only have to bear 

31:5— = 8625 lbs. Then we have m = £, ^=8625; / = 

4 
1 1.5 X 12 = 138 ins. ; n = \\ f— 1000; b = 6 in. Substituting 

and finding value of h, we have \ X 8625 X 138 = \ X 1000 X 
6 X h* ; .". h* = 297.56 ; .\ h — \"]\ ins., the depth of the beam ; 



JOINTS AND FASTENINGS. 301 

from this each stringer should be composed of two pieces 

6 X I7i ins. This gives a little greater depth than the actual 

practice, on account of the large factor of safety used, or what 

is the same thing, the small value of / and the large value 

given to W. The actual dimensions in practice are 6X14 ms - to 

6X15 ins. For longer spans the calculation in every respect 

would be similar, but, owing to the difficulty of getting good 

sound sticks over 15 to 16 ins. deep, the usual practice is when 

necessary to increase the number of stringers, as three or four 

pieces 6x15 ins. But for spans over 20 or 25 ft. long it is 

best to truss or brace the stringers ; this trussing is equivalent 

to dividing the length of the span into three parts, as shown 

in Fig. 2, Plate VII, or into two parts, as in Fig. 3, Plate VII. 

In the first case the spans are only about 8 ft. long, and in the 

second 12 ft. in a 25-foot span ; so it is evident that in this 

•case no increase in the size of the stringers will be required. 

The struts in the bracing will have to bear the load on only 8 ft. 

of span or 48,000 lbs., and being four in number, each will 

have 12,000 lbs., or at 250 lbs. per square inch there will be 

necessary 48 sq. ins. in each strut, or a single piece 6x8 in. 

In the second case the tension-rods under each stringer will 

have to carry a load on 12 ft. of span or 72,000 lbs. and on 

each stringer 36,000 lbs. ; but this passes from the middle 

through the rods on both sides to the end, the rod has only 

to bear 18,000 lbs. of load. This produces a pull or tension on 

the rod equal to the load multiplied by the length of the rod 

12.25 

and divided by its vertical reach, or 18,000 X = 99,000 

2.25 

lbs. The tensile strength of iron is about 50,000 lbs. per square 

inch, and with a factor of safety of 4, 12,500 lbs., there results 

99>°°_ _ g sq. ins. nearly, or a single rod 3 in. diameter or 2 

12,500 

rods 2\ in. diameter each. The pull on these rods tends to 

crush the end of the stringer. Large washers should be used to 

keep the pressure in safe limits. An iron plate 12 X 6 in. = 

72 sq. ins. would reduce the unit of pressure to about 1400 lbs., 



202 A PRACTICAL TREATISE ON FOUNDATIONS. 

which would be safe. Increasing the length of the vertical 
decreases pull on the rods. 

71. The writer has entered into considerable detail, as 
it shows the principles of calculating the several kinds of 
strain, determining the sizes of the different members and the 
proper construction and connection of the parts, so as to 
keep the unit strains within safe limits, and are equally appli- 
cable to bridges, trestles, floors of warehouses, etc. The 
formula above used is general, easily remembered, and easily 
applied when the principle of the lever or moments is under- 
stood. The amount and distribution of the load and the 
way in which the beam is supported are known. In the 
formula mWl = nfblf, m is a constant depending upon the 
distribution of the load and the manner of supporting the 
beam ; W'vs, the total load on the beam ; / is the clear span or 
unsupported length of the beam ; n varies with the shape of 
the beam, and for beams of square or rectangular cross-section 
is equal to \ ; b = breadth of beam ; h = depth, — all dimensions 
in inches ; f the modulus of rupture, which varies from 10,000 
to 5000 lbs. ; but only \ to T ] ¥ of these amounts should be used 
in practice. For a beam supported at one end and loaded at 
the other, in = 1 ; uniformly loaded, m == % ; supported at both 
ends and loaded with a single weight at the centre, m = % ; and 
uniformly loaded, m = %. These are common and usual con- 
ditions. If we know b and k, we can then find W \ or knowing 
W, as in the examples above, we can find h by giving a value 
to b, or find b assuming h. This will be sufficient for the pur- 
pose now considered in this volume. In the case of a joist in a 
floor, each joist supports the weight on an area of the floor 
equal to the length of the joist multiplied by the distance from 
centre to centre of the joist. The same is true for the flooring 
of a highway bridge. The load is generally taken as that of a 
closely packed crowd, and estimated at from 50 to 100 lbs. per 
square foot of area. For a warehouse floor the actual weight 
of grain, salt, or other material that can be used must be de- 
termined, and the allowance per square foot thereby determined 
in each. It will be observed that the uniform load on a beam 



JOINTS AND FASTENINGS. 203. 

has the same effect at the centre as a single load at that point of 
half of the amount ; therefore, making W = f of the total uni- 
form load, the formula reduces to \Wl = -? ,orW=- 



6 / ' 3 / 

for a beam fixed at one end and uniformly loaded. The 
general formula reduces for the four usual conditions of load- 
ing to 

W= R~7~> fi xe d at one end and loaded at the other. . (1) 

W= - J — 4t * " " * « uniformly. . . (2) 

2fbk* 
W— — j-, supported at both ends and loaded at centre. (3) 

4/3*" 

W=---j- " " " " " " uniformly. (4) 

The value of /"is taken from tables. It is important to note, 
when using the tables, in what units /, b, and h are expressed, 
as / is sometimes in inches and at others in feet, and the value 
of /"is given to correspond. In this volume /, b, and h are ex- 
pressed in inches, and /"varies for timber from 250 to 1500 lbs., 
according to degree of safety required, and in general it will 
be from \ to T x ¥ the ultimate resistance. The value of. W will 
be then the safe load. 

72. Timber may be subjected to several kinds of strain. 
1st. Crushing or compressive. 2d. Tearing or tensile. 3d. 
Transverse or bending ; which may result in breaking across the 
grain. 4th. Shearing ; a cutting or splitting along ^r across 
the grain. 5th. Twisting strain or torsion. The coefficient or 
modulus of resistance is different for each kind of strain, and 
of course varies with the kind of material. Mr. Rankine gives 
for oak and pine timber, for either crushing, tearing, or trans- 
verse strain, 10,000 lbs. per square inch, as the ultimate resist- 
ance. Green timber is' not more than half as strong as seasoned 
timber. The resistance to crushing along the grain is not 



204 A PRACTICAL TREATISE ON FOUNDATIONS. 

more than half to two thirds its tenacity or resistance to tear- 
ing. The resistance to shearing along the grain, 600 lbs. per 
square inch for pine and 2300 lbs. per square inch for oak. 

Mr. Trautwine gives the following table of the ultimate 
strength per square inch. Green timber is inserted at about 
two thirds that seasoned.* 



To 


resist 


crushing when 


seasoned, 


6,000 lbs 


per sq. in 


. oak or pine 


" 


ci 


" " 


green, 


4,200 ' 


t II 


tt cc 


CI 


•1 


tearing " 


seasoned, 
green, 


10,000 ' 
6,666 


( IC 

I it 


CI II 

tt 1$ 


a 


tl 


cross-breaking 

CI 


when seasoned, 
" green, 


10,000 ' 
6,666 


■ CI 

t CI 


oak. 


tt 


tt 


CI 


" seasoned, 


8,100 ' 


t tl 


white pine. 


<< 


" 


cc 


" green, 


5.400 


I It 


a 


cc 
■ 1 


<< 
11 


• ( 

• I 


" seasoned, 
" green, 


9,900 ' 
6,600 ' 


t it 

f it 


yellow pine 


if 


ci 

<< 


shearing, 

CI 




750 
500 ' 


t it 


oak. 
pine. 



These being ultimate or breaking strains, the safe strain 
should not exceed one fifth of these values, and for heavy rolling 
loads not more than from one eighth to one tenth of these 
values. 

73. The strength to resist tearing is independent of the 

length of the member, if the joints and connections are properly 

made and proportioned. But to resist crushing the strength 

decreases rapidly with the ratio of the length to the least 

dimension of the member ; and when its length is from 20 to 

25 times its least dimension, its resistance to crushing is reduced 

to 2000 or 2500 lbs. per square inch. But in this case a special 

^000 
formula should be used, such asa/= jj. /= length 

I_h 25o^ 
of column in inches, d the least side of the column in inches, 
and w the ultimate crushing resistance per square inch. We 

* If / in formula? i, 2. 3, 4 on preceding page, is in feet, the ultimate resist- 
ance to cross-breaking in this table must be divided by 18 in order to obtain the 
value of/, which must be further divided by factor of safety to obtain safe load. 



JOINTS AND FASTENINGS., 20J 

may therefore conclude that for perfect safety the following 
values should not be exceeded, in pounds per square inch : 

To resist crushing for a steady load, 1,000 lbs. ; for a rolling load 500 lbs. 

" " tearing " " " 1,250 " ; " " " 700 " 

" " cross-breaking for a steady load, 1,250 " ; " " " 700 " 
" " shearing, 185 to 125 lbs. 

BILL OF MATERIAL. 

74. Take, for example, a four-story trestle of the M type, 

span 30 ft. long (which, all things considered, is probably the 
most economical), mortise -and -tenon joint, total height of 
bent 100 ft. (See Plate IX, Fig. 1.) 

Timber. 

2 guard rails 6" X 6" X 25' = 150 ft. B. 1VL 

25 cross-ties 6" X 8" X io' =1,000 " " 

4 stringers 7" X 15" X 25' = 875 " " 

2 bolsters 10' X 16" X 6' = ifio " " 

6 lateral bracing 4" X 4" X 9' = 72 " " 

Fourth Story. 1 cap 12" X 12" X 10' = 120" " 

4 main posts 12" X 12" X 17.5' = 840" " 

2X braces 2" X 10" X 23' = 77 " " 

4 longitudinal braces 8" X 12" X 33' = 1,056 " " 

4 struts under stringers. .. 8" X 12" X 20' = 640 " " 

2 straining-pieces 7" X 12" X 9' = 126 " '* 

Third Story. 1 cap 12" X 12" X 17-5' = 210" 

3 main posts 12" X 12" X 20. 5' = 738 " " 

2 " braces 8" X 12" X 20.5' = 328" " 

2X " 2"Xi2"X2 9 .5' = 118" 

8 longitudinal braces 6" X 12" X 31' = 1,488 " " 

Second Story. 1 cap 12" X 12" X 23.2' = 279" " 

4 main posts 12" X 12" X 25.5' =1,224" " 

2 " braces 8" X 12" X 25.5' = 408 " " 

2X " 2" X 13" X 33.o' = 143" " 

8 longitudinal braces 6" X 12" X 31.0' =1,488 " " 

First Story. 1 cap 12" X 12" X 320' = 384" " 

2 main posts 12" X 12" X 34 7' = 833 " " 

2 " " 12" X 14" X 34-o' = 952" " 

2 " braces , 8" X 12" X 34.7' = 555 " " 

2X " 2" X 12" X 51-5' = 206" " 

longitudinal braces 

bottom sill ! 12" X 12" X 43-8' = 426" " 

Total timber 14,896 *' " 



-206 A PRACTICAL TREATISE ON FOUNDATIONS. 

Iron. 

5 bolts for guard rails. ... 1" X 14" 4 lbs. 
40 spikes " " " ....10" 22 " 
50 " " " " ....10" 28 " 

8 bolts for stringers f" X 16" grip. 16 " 

8 cast packing spools 16 " 

4 bolts for bolsters f" X 25'' " 15 " 

6 " " straining pieces |" X 27" " 60 " 

5 " «' struts \ " X 24" " 30 " 

" " foot plates 

24 " " long, braces. . . f " X 24" " 90 " 

6 " " X braces f" X 16" " 13 " 

4 " " " " f " X 14" " 7 " 

8 drift or rag bolts £ " X 20 ' " 24 " 

325 " 
4 lateral brace rods 1" X 6' 2^" grip, 66 " 

Total iron 391 " 

The total iron should also include the weight of nuts and 
washers. Either cast or wrought washers may be used. Al- 
lowing 2 lbs. for head, nut, and washer for each bolt, the 
aggregate iron would be 555 lbs. Allowing $30 per 1000 for 
timber framed and 5 cents per lb. for iron, the above bent 
would cost $475, or per foot $15.83. 

75. This calculation has been made on the M form of 
trestle (see Figs. 1 and 2, Plate IX), which shows elevation, 
plan, and details. It is probably as light a trestle as would be 
good practice for spans 25 to 30 feet long and 100 feet high. 

76. The bill of material is given purely as an illustration. 
Any other form of trestle can be similarly calculated, and 
comparison as to cost made. It is better in approximate esti- 
mates to overestimate a little than to underestimate. 

77. The writer does not give the extended tables, usually 
given in books, of the strength of materials, nor the vary- 
ing results of different experiments on the same material. 
It has been his sole object to mention those timbers in com- 
mon and every-day use, that are likely to be used in the kind 
of structures considered, and only to give those values of the 
coefficients of strength which seem to be universally accepted 
as fair working values hi actual practice. Extensive tables 
are given by Rankine, Trautwine, and other authors. 



TIMBER PILES. 20y 

Article XLII. 

TIMBER PILES. 

78. PILES are used in such materials as are not able to 
bear the weight of structures, after spreading the base of the 
structure by the use of concrete or timber, either singly or 
combined, or where the cost of thus preparing the foundation 
would be excessive, and also where, although the material is 
firm enough to bear the weight, there is danger of it being 
scoured out by the current, thereby undermining and endan- 
gering the structure, and often without considerations of the 
above nature, but purely on account of convenience, expedi- 
tion, and economy. Piles are either short or long sticks of tim- 
ber, generally round, sometimes and for special purposes sawed 
square, or rectangular as in sheet-piles. They are driven 
into the ground to a greater or less depth, depending on 
the purpose for which they are used. Oak, pine, cypress, and 
elm, are the principal trees used for piles. Oak has the advan- 
tage of being hard and tough, will stand more hammering, but 
cannot be obtained as large or as straight and as long as either 
pine or cypress ; is somewhat more expensive in certain 
localities, mainly on account of the cost of transportation. 
On account of its heaviness it is apt to sink in water, 
and large rafts are liable to sink unless buoyed up by some 
lighter logs intermixed with them, such as poplar. In some 
localities oak is more abundant than pine, and is consequently 
largely used. Pine can be obtained in long, large, straight 
logs, in any lengths up to 90 or 100 feet, and in diameters at 
the butt end from 12 to 18 inches or more, and from 10 to 12 
inches at the small end. The yellow pine of the South is 
hard and tough ; these qualities make it particularly useful 
for piles, and owing to its great abundance in the South and 
the fact that it can be floated in large rafts on the many 
bayous and rivers that flow through the forests, it is com- 
paratively cheap. The same may be said of cypress, but this 



308 A PRACTICAL TREATISE ON FOUNDATIONS. 

splits more easily and does not stand the hammer so well. 
Elm is considered good for the purpose also, and can be (ound 
in great abundance in some localities, but does not seem to 

O 

be used to any great extent when either of the above materials 
can be found. 

79. Piles are prepared for driving by cutting or sawing the 
large end square, bringing the small end to a blunt point with 
an axe, the length of bevel being from \\ to 2 ft. long; and, 
finally, by stripping it of its bark. This should never be neg- 
lected, certainly for that part below the ground. In soft and 
silty material there is no necessity of pointing the pile at all, 
and in fact it can be driven in better line when left blunt. A 
pointed pile on striking a root or any obstruction of the kind 
will inevitably glance off, and no available power can prevent 
it ; the blunt pile, on the contrary, will cut or break the obstruc- 
tion ; ample experience fully justifies this view. The large 
end of the pile is chamfered for a few inches from the end, so 
that a wrought-iron band from IO to 14 ins. internal diameter 
will just fit, and will clasp the pile uniformly and tightly with 
one or two light blows of the hammer. Sometimes a ring 
from 1 to \\ ins. less diameter than the pile is simply placed on 
the top of the pile and driven into it by light blows. This, 
however, is apt to split long layers from the pile, and in such 
cases the band is not put on until the pile is more or less 
battered, and then often very carelessly, and not concentric 
with the end of the pile. The first method of fitting the ring 
to the pile seems to be the best. If the end of the pile is not 
cut square and true, the blow will be received on one edge ; 
this tends to split the pile, to drive it out of line, and break 
the ring. The band should be made of the best wrought-iron, 
with metal thickness of at least I in. and 3 in. wide, carefully 
and thoroughly welded ; with every precaution the rings will 
very often break. It is difficult to make foremen put the 
ring on until the pile begins to show signs of splitting ; it is 
then too late to be of much advantage. They should be re- 
quired to put them on in the beginning, and if one breaks, 
require the broomed or battered portion to be cut off and a 



TIMBER PILES. 20Cj 

new ring put on at once. It may be easy to prevent an initial 
split, but difficult to prevent it extending when once begun. 
Unless bar iron is convenient and can be obtained readily, a 
large number of bands of different diameters should be pro- 
vided in advance, as rings after heavy and repeated blows 
will not stand many weldings. 

80. In driving piles into hard and compact materials, such 
as stiff clay, sand, and gravel, the point of the pile is often 
shod with iron. Unless this is properly done, no great benefit 
will result, and as commonly done it is of little use. The pile 
is generally brought to a sharp point ; three or four straps o£ 
iron are welded together with a sharp point, both inside and 
out ; the end of the pile is then inserted, only touching the 
straps near the upper ends: bolts are then passed through 
the straps and piles ; often only short spikes are used. Conse- 
quently, the bolts split or cut through the timber, until by the 
force of the blows the pile is made to fit the shoe, or the straps 
spread ; thus more harm is done than good. The only proper 
way is to have a blunt end to the pile from 4 to 6 ins. in diam- 
eter. The shoe should have a solid conical point, the base 
being of the same diameter as the end of the pile, and should 
fit it full and true ; the straps then extending upon the sides of 
the piles and bolted to them, the straps and bolts mainly hold- 
ing the shoe in place, the end of the pile receiving the effect of 
the blow. Such a shoe will to a great extent prevent the end of 
the pile from brooming. In such piles as the writer has seen that 
have been pulled up, he does not recall any case in which the 
lower end of the pile has split, after hard driving, even without 
shoes ; but the end of the pile would be broomed up to a 
length of 6 ins. It would be interesting and instructive if the 
ends of many piles that have driven could be examined. It is 
rare that piles are ever pulled after being once driven ; it is far 
easier to cut them off or blow them off below the bed of the 
river, by boring holes and inserting dynamite cartridges. We 
therefore know but little of the condition of the points of the 
piles, whether driven with or without shoes. 

81. We do know, however, a great deal about the effect of 



210 A PRACTICAL TREATISE ON FOUNDATIONS. 

heavy blows on the upper and exposed end of piles, and should 
be able to learn some important lessons in driving piles from 
these effects. There is always great danger of piles splitting 
unless well banded at their tops : and even this does not always 
prevent it, as piles will often show a split and a consequent buck- 
ling below the band and extending to a greater or lesser dis- 
tance downward ; but unless a senseless and useless hammering 
on a pile are required, a good band well fitted to the end of the 
pile, and the end cut square, will prevent any serious splitting. 
The brooming up of the top of the pile will take place as a rule 
whether a band is used or not; this causes the head to swell 
and bulge and the bands themselves to tear apart, and oc- 
casionally the fibres of the pile are completely crushed below 
the band. Even when piles are badly broomed, they do not 
necessarily show any decided or dangerous splits. The head of 
a pile may broom to a considerable extent without any serious 
injury to the body of the pile a foot or two below, and when 
cut off the end of the pile should show a hard, firm, uniform 
surface. This will only exist where a band has been used. If 
any great brooming results where a band is not used, splits to 
a greater or less extent will inevitably exist. The writer has 
personally superintended 8 or io miles of pile-trestling and 
numbers of pile foundations for piers and abutments in all 
kinds of material, and has more than casually observed as 
many more, and now recalls but few instances in which piles 
have split to any extent when properly banded and banded at 
the proper time, unless hit many heavy blows after evident re- 
fusal to penetrate farther, under a useless law based upon an 
equally useless formula. As, for instance, that a pile shall not 
penetrate more than ^ to % of an inch by 30 blows of a hammer 
weighing 2000 lbs. falling from 15 to 25 ft., at each blow, and 
this without apparently any regard to the depth already in the 
soil or the rapidity of the blows. The above is a liberal rep- 
resentation of a fact, and piles are hit often from 50 to 100 
blows to comply with such requirements, every blow brooming 
and crushing the head and point of the pile, and splitting and 
crushing the intermediate portions to an unknown and danger- 



TIMBER PILES. 211 

ous extent; the piles often crush between the head and the 
ground, or under water or under ground, not unfrequently break- 
ing short off. The writer ventures to assert that in all such 
cases the pile does not move at all ; the apparent penetration 
is simply due to crippling the fibres at some point, generally 
the head and foot of the pile, but often at intermediate points, 
the pile supposed to be moving -fo of an inch at a blow. How 
this infinitesimal distance can be determined or measured in 
pile-driving seems hard to be understood. Piles can easily be 
seen to bend perceptibly under heavy blows, and it would re- 
quire perfect elasticity to recover their exact positions within jfa 
of an inch, to say nothing of the shortening by brooming or 
crippling of the fibres. A pile may go from £ to \ an in. appar- 
ently for each blow in 30, and never actually penetrate the ^ 
part of an inch. 

82. The brooming of the head of the pile has the effect of 
materially reducing the force of the blow. A pile may ap- 
parently have ceased to move under repeated blows of the 
hammer, but if the broomed end is cut or sawed off, and 
then struck with the hammer, it may readily penetrate several 
inches at a blow ; but it is hardly ever the case that a broomed 
end pile is repeatedly cut off, so as to present at all times a 
hard, firm surface to receive the blow : hence formulae would 
seldom be of any practical value in determining the extent to 
which piles should be driven. There are many formulae pub- 
lished, but they can scarcely be considered as safe guides in 
settling the much-disputed point as to the penetration re- 
quired to bear any definite load, and the results of these under 
apparently the same conditions are so different that they 
would only tend to confuse. 

83. It might then be asked if formulas are of no value and 
no rules as to the penetration allowable in the last 10 to 30 
blows. How are we to determine when to stop driving a pile. 
This is a difficult question to answer directly, for many reasons : 
1. It depends to a large extent upon the overlying strata 
through which the pile has been driven. A long pile driven 
through a gritty material into a softer underlying strata will 



212 A PRACTICAL TREATISE ON FOUNDATIONS. 

have sufficient frictional resistance to bear with perfect safety 
the required load ; this resistance being reduced to minimum 
during the process of driving, but developed to its full extent 
after an interval of rest. And in the reverse case, that of a 
firm soil underlying a softer stratum, the ability of a pile to 
bear a load would be small, notwithstanding the great resist- 
ance to farther penetration. 

2. In many materials a very great resistance will be de- 
veloped when the pile has penetrated only a few feet — not a 
sufficient depth to give steadiness or stability to the structure 
or to be safe against the effects of a scouring action of the 
current. The writer drove about 2 miles of pile trestle in an 
approach to a bridge across the Warrior River, Ala., in a com- 
pact sand, and was unable with a 1800-lbs. hammer to drive 
white oak piles more than from 5 to 6 feet in the soil without 
battering the piles to pieces. Subsequently this was filled in 
with earth. A constant vibration in connection with the 
presence of water would doubtless cause more or less settling 
of such piles in the long run. 

3. Apparently the same material offers a very different 
resistance to piles driven under the same conditions. In some 
sands piles cannot be forced over a depth of from 5 to 10 feet ; 
in others they can be driven from 20 to 30 feet, and again 
light hammers from 1500 to 2000 lbs. with a high fall will not 
be as effective in driving piles in stiff clay or sand and gravel, 
or in a mixed soil, as a heavy hammer weighing from 3000 to 
4000 lbs. with a correspondingly low fall, although the energy 
of the blow is the same in both cases ; the blow with the 
high fall being largely taken up in bending and brooming the 
pile, while that with the low fall seems to coax along the pile, 
as it were. Whether this results from the fact that more blows 
can be made in the same interval of time, thereby keeping the 
pile in constant motion, rather than allowing intervals of rests, 
or from some other cause, the fact is indisputable, and greater 
depths can be reached with less damage to the pile. 

4. In driving piles in certain kinds of clay, the lateral spring 
of the pile makes a hole perceptibly larger than the pile itself, 



TIMBER PILES. 2\$ 

thereby allowing surface water to percolate along the pile, 
often as deep as the point of the pile ; and whether it ever 
gripes the pile is an unsettled question. This, combined with 
vibrations from a rapidly moving train, may ultimately cause 
settling. 

5. No rule that does not take into consideration the loss of 
energy resulting from broomed ends, the varying amounts of 
frictional resistance of different materials during the process of 
driving, and the depth of the pile in the soil, but is based 
solely on the weight of the hammer, the height of the fall, and 
the penetration at the last blow, can furnish any reliable or 
even approximate idea of either the immediate or ultimate 
supporting power of a pile or any number of piles. 

84. We must therefore rely mainly on experience, or upon 
experiment, in each particular case ; and in the absence of 
these, it is merely guess-work and taking the chances. Exper- 
iment, however, is in the reach of all, will cost but little money, 
and will take but little time ; and no excuse can be given for 
not making satisfactory tests of some kind in the absence of 
precedents in similar material or in the same locality. If ex- 
perimenting on piles in trestle work, drive a single bent or 
two bents of piles at the proper distance apart. Upon these 
construct a platform, and place weights equal to or twice as 
great as the greatest load that can possibly come upon them. 
If under this load no settlement takes place, the trestle will be 
safe, and piles in other bents driven to the same depth and to 
the same resistance in the last few blows can be relied upon. 
If, on the contrary, settlement does take place, more piles or 
longer piles must be used. Weights can gradually be added 
on a single pile until it begins to settle, and from this the num- 
ber of piles can be estimated to carry any proposed load, allow- 
ing a factor of safety from 2 to 4. Clusters of piles will how- 
ever bear more in proportion than single piles, if not driven 
nearer thar 2\ ft. centres, as they consolidate and compact the 
soil in proportion as the numbers increase in a given area. 
Such experiments should not be made for at least 24 hours 
after the piles are driven, so as to allow time for the material 



214 A PRACTICAL TREATISE ON FOUNDATIONS. 

to compact and be adjusted around the pile. The following 
is an interesting and instructive experiment made by Maj. 
E. T. D. Myers. I give it substantially in his own words, as 
contained in a letter dated Feb. 7, 1885 : 

"Bents \2\ ft. centres, 6 piles each; length, 50 ft.; Grade 
line, 15 ft. above low-water; in use fourteen years. Piles 
driven in a liquid mud. Two bents of 6 piles each were 
driven, upon which a platform was placed, and upon this a 
weight of 75,000 lbs. uniformly distributed. The experiment 
was made 19 hours after driving. 

OOOOOO Bent 18th. 

660OOO Bent 17th. 

123 456 

No settlement taking place, piles Nos. 2 and 5 in each bent 

were cut out, leaving 4 piles in each bent. Then No. 3 of 

the 17th and No. 4 of the 18th bent were cut out, leaving only 

3 piles in each bent. About 5000 lbs. was then added to the 

load, when No. 6 of 18th bent yielded, followed by No. 3 of 

the same bent, and sank until Nos. 4 and 5 were again brought 

to bear. It required, therefore, about 13,000 lbs. each to start 

the piles. The record of the driving was as follows : 

BENT 17: FALL FROM 3 TO IO FT. 

Pile No. 1, 11 blows. Last blow, 7 ft. fall, drove it 11 inches. 

9 
18 " 
17 " 
" 6 

10J " 



Pile No. 1, 12 blows. Last blow, 5 ft. fall, drove it \o\ inches. 

a "2 8 " " " 4 " " " 8 " 

it It -, g ti it H a it it it gl it 

It ti A Q ti it ti -, ti It H A It 

n a * | a tt tt a jq a il u „ U 

« «6, 5 " " " 9.8 " " " 22 " 



" 2, 


13 


n 


a 


it 


9 " 


" 3, 


8 


a 


tt 


" 


9 " 


" 4, 


8 


tt 


K 


n 


8 " 


" 5, 


9 


tt 


a 


a 


S " 


u 6, 


7 


tt 


n 


tt 

BENT 


7 " 
18. 



TIMBER PILES. 21 5 

A pile 40 ft, long, after sinking 30 ft. with its own weight 
and that of the hammer weighing 2000 lbs., was struck with 
a blow of 2-ft. fall, and then settled 6J ins. in one minute 
by the weight of the hammer. Four weeks after this a blow 
with a fall of 5 ft. did not move it. A blow of 14-ft. fall 
drove it 4^ in. Also at the Gunpowder River piles 40 to 50 ft. 
long were driven, until they did not sink more than 18 in. 
under a hammer weighing 1800 lbs. falling 20 ft. Four piles 
to the bent. In neither case was a hard stratum passed through 
or reached." This is but the common experience in the South- 
ern swamps. Even with very light falls, the penetration at 
the last blow is from 4 ins. to 2 ft. High falls are out of the 
question, as there is danger of losing both pile and hammer. 
In all cases above alluded to, these trestles have carried with- 
out settling the heavy trains of the present day. The above 
examples show the great load that piles driven to a depth of 
30 to 35 ft. in the softest material that can be called earth will 
bear. A 30-ft. pile that is 30 ft. in the soil would present on 
an average about go sq. ft. of surface in contact with the soil, 
and bearing safely 13,000 lbs. ; the frictional resistance would 
be about 144 lbs. to the sq. ft. of surface. The probabilities 
are that they would carry to at least 300 lbs. The frictional 
resistance is known to vary from 300 to 800 lbs. per sq. ft., de- 
pending upon the nature of the material into which the piles are 
driven. It will be observed in the above table that pile No. 6 
of the 1 8th bent was the first to yield under the weight of 
13,000 lbs. (This pile penetrated under a 9.8-ft. fall at the last 
blow 22 ins.) The effect of this was to throw a large portion of 
the 13,000 lbs. on the next pile in the same bent, which of 
course yielded. The greatest load that could come upon a 
span of 12^ ft. would be 75,000 lbs.; or, in a four-pile bent, 
would be 18,750 lbs., and in a six-pile bent 12,500 lbs. per pile. 

85. Some 8 miles of trestle, constructed under the writer's 
direct supervision in the Southern swamps, the bents contain- 
ing 4 piles, spans \2\ ft., depth of pile in the soil varying 
from 30 to 35 ft., the penetration varying from 6 in. to 2 ft. 
at the last blow of a 2000-lb. hammer falling only a few feet. 



2l6 A PRACTICAL TREATISE ON FOUNDATIONS. 

has carried for twenty years the heaviest trains without 
any settling. In the abutments of some of the bridges in 
these swamps the piles have carried with perfect safety 17,000 
lbs. to the pile. How much more they are capable of carrying 
is not known. In one of these abutments, piles only 30 ft. in 
the soil could not be moved by continued hammering with 
high falls a few days after driving. The experiment was 
made as the writer was not satisfied with the record of the 
original driving, and desired the piles to be driven to a greater 
depth. Finding it impracticable to move the piles he deter- 
mined to hammer one or two to destruction or move the piles ; 
destruction was the result, and new piles were driven to take 
their place. 

86. We may, therefore, conclude that piles, from 30 to 40, 
in even the softest alluvial soils, will carry, by frictional resist- 
ance alone, from 20,000 to 25,000 lbs., or 10 to 12^ tons. 
There are examples of piles driven in stiff clay to the depth of 
20 ft., that carry from 70 to 80 tons per pile; this is an un- 
necessarily heavy load, and when driven from 2\ to 3 ft. 
centres they will rarely have as much as one-half of the above 
loads to carry. There are many instances in which piles carry 
from 20 to 40 tons under the above conditions. 

87. In sand and gravel, piles will carry to the full extent of 
the crushing strength of the timber, provided the depth in the 
material is sufficiently great to prevent vibrations from reach- 
ing the point of the pile ; other considerations will require 
this depth to be at least 10 ft. or, at most, 20 ft. Any further 
hammering on piles in such materials is a waste of time and 
money, and injurious to the pile itself. To hit such a pile 100 
to 150 blows to drive it an inch, as has been done, is simply folly. 

88. Some times piles drive easily and regularly to a certain 
depth, and then refuse to penetrate farther ; this may be caused 
by a thin stratum of some hard material, such as cemented 
gravel and sand or a compact marl. It may require many hard 
and heavy blows to drive through this, thereby injuring the 
piles, and perhaps getting into a quicksand or other soft ma- 
terial, when the pile will drive easily again. If the depth of 



TIMBER PILES. 217 

the overlying soil penetrated is sufficient to give lateral sta- 
bility, or if this can be secured by artificial means, such as 
throwing in broken stone or gravel, it would seem unwise to 
endeavor to penetrate the hard stratum, and the driving should 
be stopped after a practical refusal to go with 2 or 3 blows. 
The thickness of this stratum and nature of the underlying 
material should be either determined by boring or by driving a 
test pile to destruction if necessary. In the latter case the 
driving of the remaining piles should cease as soon as the hard 
stratum is reached. 

89. Sometimes in driving piles it is difficult to keep the 
piles down after the impact of the blow is over : the piles, begin- 
ning to rise, lifting the hammer with it, and upon removing 
the hammer the piles would shoot up 5 to 6 ft. or more. This 
is, no doubt, due to a stratum of quicksand. The writer has 
overcome this difficulty by driving the piles with the butt, or 
large end, downward. This is the only case in which piles were 
driven butt downward, in the writer's experience, though some 
authorities recommend it. 

90. The above seems to cover the various conditions and 
kinds of material met with in driving piles, and, as can be 
readily seen, no general or rigid rule can be given, either as to 
the depth to which a pile should be driven into any kind of soil, 
or as to the penetration in the last blow, or last few blows. 
Experience, and experiment alone can be of any practical 
value. But enough has been said to establish, first, that when 
piles are driven in a soft, swampy material, a penetration of 
from 30 to 40 ft. into the soil will give ample support for 
ordinary purposes, regardless of the weight of the hammer, the 
height of the fall, or the penetration at the last blow, within 
limits generally existing in practice ; second, in clay, sand, and 
gravel the depth required is only that necessary to give stabil- 
ity to the structure, to get below the scour-line, or beyond the 
reach of vibrations caused by moving loads, in general, from 10 
to 20 feet ; third, that a continued hammering on piles, after 
practical refusal to go, is absolutely injurious. 

91. The following formulae are given for the benefit of those 



21 8 A PRACTICAL TREATISE ON FOUNDATIONS. 

who may differ with the opinions expressed above. Rankine 
gives the following : The energy of the blow is employed as 

follows: W/i= —p^ (employed in compressing the pile) -\- Px 

(employed in driving it), in which W =■ weight of the ram or 
hammer, h = height of fall, x = the penetration of the pile at 
the last blow, P = greatest load that it will bear, 5 = area of 
cross-section of the pile, / = length of pile, and the modulus of 
elasticity E = about 108,000 lbs. per square feet. Hence 



IaESWJu aE*S*x 2 iESx . , 

/J= V / V+^--— • • ■ (I > 

In any particular case the values of the quantities in the 
second member are all known, and P can be found. Major 
Sander's formula is as follows : 

r, h W 

; ? ^ x ? < 2 > 

in which h = fall in inches, W = weight of hammer in lbs., 
a = penetration at each blow towards the last, P = safe load 
in pounds. Trautwine's formula, 



3V/1XWX 0.0268 



(3> 



1 -\-a 

and for the safe load take one half of this value. Assume the 
weight of the hammer at 2500 lbs., penetration i|- inches at the 
last blow, or towards the last. Then from eq. (2) the safe load 

40 X 12 X 2500 

P= — r = 100,000 lbs. = tons, 

1.5 X 8 

and from eq. (3) the safe load equals 

P 3.42 X 2500 X 0.0268 

- == x 2 = 49I tons, or 99,000 lbs., 

the height of the fall being taken at 40 ft. in both cases. The 
calculation in Rankine's formula is long and tedious, and prob- 
ably no more accurate. Applied to piles driven with a hammer 



TIMBER PILES. 2 1 9 

1 200 lbs. and fall of 20 ft. penetration f in. Trautwine's formula 
gives, as a safe load, 24.9 tons, and Major Sander's 21.4 as safe 
load ; the actual load borne by the piles is 18 tons to each pile ; 
and again, piles driven only 16 ft. into alluvial mud, weight of 
hammer 1500 lbs., fall 24 ft., penetration 2 in., actually sup- 
porting 20 tons. By Trautwine's formula safe load is 19.3 tons, 
and by Major Sander's 12.06 tons, and still in another case the 
calculated safe load is 55 tons, whereas the actual load is 70 
tons. In New Orleans the piles driven from 25 to 40 ft. carry 
safely from 15 to 25 tons. This is in a soft, alluvial soil. 

Article XLIII. 

TIMBER PILES— (CONTINUED). 

92. There has been suggested recently another formula, known 

fzvJz 
as the Engineering News formula, as follows : P 



S+C 

P = safe-bearing resistance, f a factor varying from 12 to 1, 
and recommended to be taken = 2, giving a factor of safety 
of 6, w = weight of hammer in lbs., 5= penetration in inches, 
the average during the last few blows, and C taken = 1, a 
constant to provide for the increased resistance to moving at 

the moment of impact, reducing the formula to P = -^— — for 

S-f- 1 

practical use. Since writing the above pages on pile-driving, 
this formula has been brought into great prominence by rea- 
son of the learned and able discussions, as to its theoretical 
accuracy and practical reliability and usefulness, by some of 
our leading engineers. The conclusion seems to be reached 
that it is. certainly as reliable as any of its predecessors, and 
perhaps comes as near being reliable as it is practicable, 
though leaving out many important conditions and consid- 
erations, which must materially modify the relations between 
the energy of the blow and the penetration. The formula 
is simple and easy of application in any particular case. 
The writer, however, sees no reason to modify the already 
expressed opinion that the ultimate bearing resistance of 



220 A PRACTICAL TREATISE ON FOUNDATION'S. 

piles cannot be expressed even approximately in terms of 
the weight, fall, and penetration ; and even if approximately- 
true for one kind of material and one set of conditions 
usually attending the driving, they would miss by very far the 
mark when applied in case of another material and under 
other conditions. And especially as his experience has been 
confirmed during these discussions by the statements of many 
prominent engineers as to penetration at the last blow, one 
engineer stating that piles about 40 ft. long sunk with their own 
weight and that of the hammer the full length of the pile, and 
could not be driven at all after a period of rest ; that they have 
carried ever since the heavy trains used on the road. 

The writer has sunk piles from 6 to 10 ft. simply by work- 
ing the piles backward and forward ; two such piles to the 
bent carried safely a construction train, loaded with rails and 
ties, for many months without any evidence of settling. 

93. After a period of rest it is evident that piles support 
their loads by the upward pressure at the point of the pile and 
by the frictional resistance on the surface of the pile in contact 
with the soil. The relation between these resistances and the 
weight that the pile can carry can be simply expressed as fol- 
lows : w =p -\-fs, in which w = the safe-bearing power, p = the 
safe resistance to settling determined by the bearing power of 
the material, f a factor depending upon the frictional resist- 
ance of the material on the surface of the pile, 5 = number of 
square feet of surface in contact with the soil.* If we knew/ 
and f in all cases, and the load to be carried, we could deter- 
mine the depth of one or a group of piles below the surface 
necessary to carry the load. The value of p is already known 
approximately for ordinary materials, and for sand, gravel, and 
clay is universally recognized as safe at 5000 to 6000 pounds per 
sq. ft., and for silt can be taken at zero. The value of /"can be 
determined with the same degree of accuracy as is now used 

* There is no other formula applicable to the bearing power of piles sunk by 
the water jet, or worked into the ground by a to-and-fro motion, or when driven 
30 or 40 ft. into the soil by three or four blows with a hammer falling three or 
four feet. 



TIMBER PILES. 221 

and considered safe in the usual coefficients of friction, and at 
a comparatively small cost ; and, in the absence of more reliable 
information, it could be taken at from ioo lbs. in the softest 
semi-fluid soils to 200 lbs. per square foot in compact silt and 
clay, and from 300 to 500 lbs. in mixed earths with consider- 
able grit, and from 400 to 600 lbs. in compact sand, and sand 
and gravel. Assuming, then, that we were driving piles for a 
trestle, 4 piles to the bent, bents 14 ft. apart, and assuming the 
equivalent uniform load to be 6000 lbs. per foot, each pile 
would have to carry 21,000 lbs. 

In the silt of the- swamps, with/ = o and/= 150 lbs. the 

iv — p 
formula gives : s = — — = 140 sq. ft. of surface, a pile 

averaging 11 ins. diameter contains 2.8 sq. ft. per foot of 
length, and should therefore be 50 ft. in the ground. The 
writer is satisfied that a bent of four such piles, especially if 
the outside piles batter, would safely carry the load. If con- 
sidered risky, put in a centre pile, reducing the load per pile 
to 16,800 lbs. 

2. When driven in clay, p = 5000 lbs., and/= 150 lbs., 
each of the four piles would have only to carry fs =w — p = 
21,000 — 5000 = 16,000 lbs. by frictional resistance, hence s = 
106 sq. ft., or depth in the ground = 38 ft., and if /= 200 lbs., 
s = 80 sq. ft., and the depth in the ground 30 ft. No one 
would question that ample safety is secured in this case, and in 
fact 15 to 20 ft. in the ground would be perfectly safe. 

3. In compact sand, p = 5000, / = 500, s = 32 sq. ft. and 
depth in the ground = 12 ft. nearly. This would answer in 
any case, unless danger from scour exists. On any reasonable 
values oip and/, the above formula, I think, would certainly 
be equally as reliable as any other, and certainly comports 
better with the actual existing conditions, and with a fair 
number of practical tests similar to those already described, in 
varying soils, would give us as fair a standard of comparison, 
as now exists in the case of retaining walls, timber, and iron 
columns and beams, which are based upon experimentally 
determined constants. 



222 A PRACTICAL TREATISE ON FOUNDATIONS. 

93.V. We can, then, conclude that the bearing power of 
piles will vary from 13,000 lbs., or 6£ tons, to 140,000 lbs., or 70 
tons, according to the character of the material into which they 
are driven ; and this, reduced to frictional resistance per sq. 
ft., for a pile driven 30 ft. into the soil, gives from 140 lbs. to 
1550 lbs., which may be taken as the extreme limits, and from 
200 to 800 lbs. may be taken as good working limits, not to 
exceed the smaller, in alluvial and soft soils, nor the greater, 
in the firmer materials, such as stiff clay, sand, and gravel or 
mixed materials. 

94. The usual mode of driving piles is by means of the pile- 
driver, which consists essentially of 2 horizontal pieces of tim- 
ber, 10 X 12 ins. or 12 X 12 ins., and 10 to 18 ft. long, placed 
about 3.5 ft. apart, connected by short struts and tie rods; 
near one end of these, two uprights, 6 or 8 ins. by 10 ins. and 
from 20 to 40 or more feet long, are connected by cutting 
shoulders in the ends, so as to fit the horizontal pieces, to which 
they are also fastened by bolts. In the rear of the verticals 
bent iron bars are placed, the ends passing through the 
uprights or leads ; these act as braces for the leads, and also to 
hold the wedges necessary to keep the piles in place and 
straight. These are placed at intervals of from 6 to 8 ft., ver- 
tically; on top of the leads a strong cap of oak or some hard 
wood 6 ins. thick and 12 to 15 ins. broad, is placed and con- 
nected by mortise and tenon and iron bolts. A ladder runs 
from the other end of the horizontal frame nearly to the top of 
the leads to which it is bolted ; at intervals horizontal pieces 
connect the ladder and the leads, upon which planks are placed 
for platforms. On the inside of the leads a strip of hard 
wood 2^ to 3 ins. square is bolted at close intervals, and on the 
face of these-strap iron •£ in. thick is bolted, the heads of the 
bolts countersunk. A cast-iron hammer of the required weight, 
varying from 1000 to 4000 lbs., is cast with grooves on the 
sides, so as to be held in place by the strips, and at the same 
time to slide freely on them. A rope is attached to the upper 
end of the casting, and passes through a hole bored in the cap. 
and over a pulley fastened on top of the cap, thence downward, 



TIMBER PILES. 223 

passing through a snatch block at the bottom, and thence 
horizontally to a drum or capstan ; this is now the ordinary 
arrangement, the rope being permanently fastened to the ham- 
mer. The second plan is to attach the rope to a heavy double 
block of wood, into which is framed a pair of nippers, with the 
upper ends curved outward, and the lower ends with pyramidal 
points and square projecting shoulders on the inside ; these are 
so suspended on a strong bolt that the lower ends remain in 
contact, and are only opened by closing the curved upper ends. 
The top of the hammer has a wedge-shaped projection with 
square shoulders a few inches from the top of the projection. 
The block is also framed so as to slide down the strips on the 
leads by its own weight, when, in falling rapidly on the ham- 
mers, it takes hold of the projection, when the power is 
applied it lifts the hammer with it, when it comes in con- 
tact with bevelled blocks fastened to the leads near the top, 
the curved upper ends are gradually closed, the lower ends 
open, and the hammer falls ; the block again descends rapidly 
and clutches the hammer as before. The leads are braced 
laterally, by inclined struts resting against horizontal pieces 
projecting on either side, and the rear end of the horizontal 
frame must be weighted or held down, so as to counterbalance 
the weight of the hammer. The first method, in which the 
rope is attached directly to the hammer, has many advantages ; 
more blows can be struck per minute, the height of fall can be 
more easily regulated and changed, being dropped at any de- 
sired distance above the top of the pile, and there is no danger 
of losing the hammer if the pile should spring out of the leads 
or be driven below them. (See Plate V, Figs. 1, 2, 3, and 4.) 
95. Such is the simple pile-driver. On firm ground it can 
be moved from point to point by letting it rest on hardwood 
rollers attached to the under side of the horizontal frame, these 
rollers being turned by levers inserted in holes bored into 
them. On softer ground a platform of timbers can be laid, on 
which the driver rests and is moved. This is a slow method, 
and where any great distance is to be passed over it is best to 
fasten the driver to a platform made of strong timbers, upon 



224 A PRACTICAL TREATISE ON FOUNDATIONS. 

which also the engine and boiler can be placed, the whole 
then resting on strong timbers, to the under side of which iron 
bars or rails are fastened. This is elevated on a level with the 
top of the piles, the leads project beyond the platform a dis- 
tance equal to the distance between the bents, say \2\ feet; 
the two centre piles of the bent can then be driven. The 
driver is moved forward a few inches, the frame holding the 
leads can be turned on a pivot, and the two outside piles driven 
in a proper line with the inside ones. These piles are then cut off 
and capped, temporary stringers placed in position, iron cast- 
ings with erooved rollers fastened to the stringers, upon which 
the rails run, and by ropes attached to the bent and the drum 
of the engine the driver is pulled forward into its new position, 
and another bent driven as before described, and so on. In a 
more perfect form the driver is attached permanently to a 
platform or railway car, and as the work proceeds stringers 
and rails are temporarily laid, and the car run forward on these. 
For the repairs of completed roads, drivers of this kind are used, 
the leads being hinged so that when not in use they can be 
lowered, so as to pass through bridges, tunnels, etc. For driv- 
ing piles in water the driver is simply fastened to a barge, and 
floated to its position, controlled, held, and moved for short 
distances by means of anchors. Piles can be handled more 
readily and more economically on water than on land, but it 
is more difficult to place and hold the driver when floating, es- 
pecially if the current is rapid, or in high winds. The cost of 
driving piles should not exceed 8 or ten cents per lineal foot of 
pile. The cost of piles vary from 9 to 12 cents per lineal foot. 
96. The power used in pile-driving is either man, horse, or 
steam power. The first is not often used. It is necessary to 
have a light hammer and a low fall. A number of men take 
hold of a rope, lift the hammer a few feet, and then all let go 
at the same time ; it is a slow process, and not calculated to 
obtain the best results. 

Horse power is very common on land, and can be used on 
water; the rope is fastened to a capstan, which can be readily 
made by any carpenter ; a long lever is attached to a centre 



TIMBER PILES. 22 5 

post, to which a horse is attached, and as the horse moves the 
rope is wound around the capstan, and the hammer is lifted ; 
at the proper moment the capstan can be thrown out of gear, 
and the hammer falls. Good and rapid work can be done in 
this manner. 

But when a large number of piles are to be driven, steam 
power is mainly used ; the rope is attached to an iron spool 
connected with the engine, around which the rope is wound as 
the power is applied, and by throwing it out of gear the ham- 
mer falls. This is the most rapid and expeditious method, 
and admits of very heavy hammers being used. 

There is also a steam-hammer pile-driver, in which the blow 
is struck by a hammer attached directly to the piston of an 
engine. In this very powerful and rapid blows can be struck, 
and doubtless it has many advantages ; but it is not in common 
use, and in fact it is seldom seen, and therefore it can be pre- 
sumed to be less economical than the ordinary drivers. 

97. None of the drivers above mentioned can be used to 
drive piles inclined to a vertical without great inconvenience 
and delay, but it is often desirable to drive piles on a batter, this 
method possesses a great many advantages in driving piles for 
trestles, as will be shown in another paragraph. A pile-driver 
is constructed for this purpose somewhat differently from those 
described above. Instead of the leads being fastened to the 
horizontal frame, they are supported by strong heavy bolts, 
attached to an iron frame, which is fastened to the horizontal 
frame, the leads being free to turn about the iron bolt through 
an arc of many degrees, by which means the leads are inclined 
to the vertical, and the pile can be driven in the desired direc- 
tion with the same rapidity as in other cases. The construc- 
tion of such a driver is as simple as those used in driving only 
vertical piles, and should be used more generally than it is. 
The drawings, Figs. 1,2, 3, and 4, Plate V, show the general 
construction of pile-drivers. 

98. When for any reason it is necessary to sink piles to a 
great depth in a firm and compact material, without injury to 
the piles by many heavy blows, it can be done by the use of 



226 A PRACTICAL TREATISE ON FOUNDATIONS. 

the water-jet ; a pipe can be attached to the side of the pile 
either fitting in a groove cut for the purpose or fastened to the 
outside ; this pipe ending in a nozzle at the point of the pile, 
the upper end attached to a force pump by a hose. When 
the water is forced through this pipe it removes or loosens 
the material around and under the point of the pile, which 
sinks by its own weight, or a weight is placed on top, or aided 
by light blows from a hammer. This is a rapid and effective 
mode of sinking piles, and has been used to a large extent and 
with satisfactory results. It should be infinitely preferred to the 
practice of long-continued and heavy blows to drive a pile a few 
inches. Piles have been sunk to great depths by this process ; 
it is an application of the same principle as has been fully ex- 
plained in sinking the Cushing cylinders and in making borings 
for foundations. An oblique hole is sometimes bored into the 
pile near the bottom, so as to discharge the water exactly at 
the point of the pile ; but this does not seem to be necessary, or 
even to possess any material advantage ; a few blows should be 
given after stopping the water-jet. It is of great advantage in 
sinking iron pipes to rock for the purpose of submarine blasting, 
or for columns composed of iron cylinders, as well as in sinking 
screw-piles, which will be explained under that heading.* 

Article XLIV. 
USES OF PILES. 
99. PURPOSES for which piles are used will now be discussed. 
Piles are divided into long and short piles, or piles to bear 
directly and entirely the load, and piles the main object of 
which is to compact a soft and loose material so as to increase 
the bearing power of the soil. Short piles or those used for 
the latter purpose are from 8 to 15 ft. long, and generally from 
8 to 10 inches in diameter; these are used principally to sup- 

* Piles were recently sunk with the water-jet to the depth of 25 ft. in sand. 
It is stated that it only required two minutes to sink each pile. Bowlders under 
the points of piles were carried down with the piles by sinking a pipe to the 
under side of the bowlders and using two water-jets at the same time. These 
piles could not be moved by blows from a heavy hammer only a few minutes 
after stopping the flow of water from the pumps. 



TIMBER PILES. 



227 



port the walls of houses and other comparatively light struct- 
ures. In some sections of the country, especially in the 
Southern cities, the soil is of a soft alluvial material, and in its 
natural state is not capable of bearing heavy loads. In such 
cases trenches are dug, as in firmer material, and a single or 
double row of short piles are driven close together, and under 
towers or other unusually heavy portions of the structure the 
•area thus to be covered is filled with these piles ; the effect of 
this is to compress and compact the soil between the piles and 
to a certain extent around and on the outside, thereby increas- 
ing its bearing power, whatever resistance the piles may 
offer to further settlement may be added, though not re- 
lied upon. These piles are then cut off close to the bottom of 
the trench, and generally a plank flooring is laid resting on the 
soil and piles, or a layer of sand or concrete is spread over the 
bottom of the trench to the depth of 6 ins. or 1 ft., and the 
structure whether of brick or stone commenced on this. There 
is little or no danger of such structures settling, and if they do 
the chances are that they will settle uniformly if the number 
of piles are properly proportioned to the weight directly above ; 
but if the same number of piles are used at all points of the 
structure, although considerably great weights are on some 
walls or some parts of a wall, unequal settlement may take 
place, causing ugly or dangerous cracks in the structure. 

100. A modification of this plan is to drive a pile into the 
soil and then withdraw the pile and fill the hole thus formed with 
sand ; this being done at intervals of 2 or 3 ft. under the walls of 
the structure as above described and all of the holes filled with 
sand, there results a good foundation. The columns of sand are 
called sand-piles, owing to the great mobility of the sand 
grains ; they act somewhat as in a fluid pressure, pressing equal- 
ly in all directions at any given depth, and therefore afford a 
better support than the wooden piles, and have the further ad- 
vantage of being permanent. The wooden piles, unless constant- 
ly wet, will rot sooner or later, and although timber constantly 
wet does not rot, yet it becomes more or less softened and 
soppy and loses some of its original strength. 



228 A PRACTICAL TREATISE ON FOUNDATIONS. 

Short piles are also used under small piers and abutments 
for the same purpose as above mentioned, but should not be 
used where very heavy weights are to be carried, or where they 
can be reached by vibrations caused by rapidly moving trains ; 
in such cases long piles should be used. 

IOI. Long piles vary in length, from 15 to 100 ft. and in 
diameter from 12 to 18 ins. or more; and although their re- 
sistance to settling is increased by compacting the soil, the 
load is supported generally, though not always, directly by the 
pile, and the weight does not come upon the soil between them 
or around them at all. Such piles are always used when great 
depths are. to be reached below the ground or water-surface, or 
where there is any danger of the material around them scour- 
ing out — as under very large and heavy piers and abutments 
in rapid currents, or in very soft materials ; also, where piers or 
abutments are built on or near to the edge of steep banks 
which are in danger of caving in, under the action of rising and 
falling water, although the material itself may have ample 
supporting power. This is the case along many rivers, notably 
the Ohio, whose banks cave in regularly and annually at very 
many points, unless protected by stone-paving or vegetable 
growth, willow trees, etc. Should such banks cave under the 
piers, broken stone could be thrown in and around the piles, 
thereby securing the structure. They are also used in con- 
structing wharves, dykes, etc., for the main piles in coffer 
dams, and to a very large extent in building railroads across 
swamps, bayous, sloughs, etc. In driving piles under piers and 
abutments, the piles are driven in rows about 2\ feet from 
centre to centre of piles in all directions,, over the entire area to 
be occupied by the structure and one row on the outside, mak- 
ing the area about \\ to 2 feet larger all around than the bot- 
tom of the structure itself. After driving the piles they can 
be cut off at or above the bottom of the excavation, and upon 
these caps of 12 X 12 ins. timber are placed and drift-bolted, 
another layer of timber placed at right angles, and on top of 
this another layer of timber or plank, all bolted or spiked to- 
gether, and the masonry started on this. All of the timber should. 



TIMBER PILES. 229 

be under the lowest low-water, so as to be constantly wet ; in 
this case the piles bear the entire load. Sometimes concrete 
broken stone, or gravel is placed around the heads of the piles 
and around and between the timbers of the platform, and 
again the timber may be entirely omitted and concrete placed 
around and over the piles to a depth of at least 2 feet. In the 
last two cases a part of the load is borne by the compacted 
soil between and around the piles. Opinions differ as to which 
is the better: both are good enough ; but unless the timber is 
wet it would seem better to leave it out, though some authori- 
ties say that timber imbedded in cement concrete will last as 
long as when constantly immersed in water. If so, the first, or 
rather the combined timber and concrete, would be preferred. 
Both methods are in common use. 

102. In the construction of wharves, piles are driven in rows 
extending well out into the water ; the distance apart of the 
piles and the depth to which they must be driven depending 
entirely on the load which they have to bear. These are cut 
off a few feet above the water surface, capped with square 
timber 10 X 12 ins. or 12 X 12 ins., upon which joists are placed 
at close intervals, and on these a plank flooring of hard wood 
3 ins. thick. Each pile in such cases supports an area whose 
sides 'are respectively the distance between the rows and be- 
tween the piles in each row — a fair average being 5 ft. each 
way, or an area of 25 sq. ft., as very heavy loads are often con- 
centrated over small areas. The proper area is, however, easily 
determined when the greatest load per square foot is decided 
upon. These piles will soon rot above the water-line, when they 
must be cut off, and framed bents of timber constructed on them. 
The spaces are, however, often filled up with earth, gravel, or 
shell, and only a timber wall or bulkhead must be maintained at 
the outer end to hold the material in place. This consists of a 
timber crib resting on two or three rows of piles, tied back 
into the embankment by long timbers notched and bolted to 
the crib timbers. In front fender piles are driven and fastened 
to the crib by iron straps or bolts, and projecting above the 
wharf 4 or 5 ft. The bulkhead should be strong and heavy 



23O A PRACTICAL TREATISE ON FOUNDATIONS. 

and well anchored to the earth as the weight of the material 
behind and the load upon it exerts a great force, tending to 
force it outward ; it would be better to drive the piles under the 
crib, slightly inclined backward, so that the resultant pressure 
would be nearly in the direction of their length. On important 
water-fronts, masonry or concrete walls or bulkheads are con- 
structed and faced with timber, against which boats or vessels 
(.an rest. Bulkheads are subjected to severe blows and shocks 
from vessels. Such constructions are used along the foot of 
embankments, to prevent caving and sliding. 

103. Dykes or jetties are formed by double rows of piles, 
driven at right or acute angles with the direction of the cur- 
u-nt, sheeted as in ease of walls of coffer-dams, and filled with 
gravel, stone, or shells. When driven at a slight inclination to 
the current the)- serve to force the water through a narrow 
channel, and the increased velocity scours the material of the 
bed of the river, depositing it behind the jetties or in the 
deeper water below the mouth of the jetties. When at a large 
or a right angle to the current they serve the same purposes. 
They should not be built too high above the low-water surface. 
These subjects, however, more properly belong to river and 
harbor improvements, and are merely alluded to incidentally. 

104. The more extensive use of piles for foundations is in 
the construction of trestles across swamps, bayous, etc. There 
.ire two methods practised; one is to drive piles in rows of 4 
or 6 each, the rows being from 10 to 25 ft. apart, the position 
of the piles in each row or bent being regulated so as to be under 
the posts of the structure above. They are then cut off a little 
below low-water or the moisture surface, and upon these framed 
trestles of any height aiul of any of the forms above described 
are constructed and fastened to the piles by straps or bolts. 

This has the advantage of placing the piles where they will do> 
the most good, and of utilizing the full length of pile to support 
the load by direct bearing or by the frictional resistance of the 
soil. In the second ease the piles are allowed to project above 
the ground or water and then cut off; the caps resting directly 
upon the tops of the piles, to which they are fastened by bolts 



TIMBER PILES, 23 1 

or straps. This method is hardly applicable when the heighl 
of the trestle is more than 20 to 25 ft. above the ground or 
bed of the streams, owing to the greal length of piles required, 
and the further fact that the piles are driven vertically, and 
consequently would nol have breadth of base sufficient to 

provide lateral stability, and it is therefore limited to heights 
of trestle rarely exceeding 15 ft. above the ground. This is 
generally as greal a height as will be required above the 
swamps, and commonly not more than 5 to 10 ft. When no 
batter-posts are used, the common construction in a. 4-pile bent 
is to drive the two inside piles about 5 ft. eentres, so that: they 
may be directly under the rails, and the outside piles 2^ ft. from 
these on either side; making the total distance from outside to 
outside of piles from i2 to 13 ft. This requires caps about 14 
to 15 ft. long, generally fastened to the piles by drift-bolts. 
Upon these stringers, cross-ties, and guard-rails are placed sim- 
ilarly in every respect to those of framed trestles. Hut often 
additional Stringers are placed over the outside piles, and long 
cross-ties 13 to 14 ft. long are used. This requires a consider 
able increase in the quantity of timber and iron, with hardly any 
compensating advantages, as seen by the following comparative 
estimate. For a single span, 12^ ft., we have 

1 cap 12 X 12 in. X 14 n if>8 ft. B. M. 

4 stringers 6 X 14 in- i2i ft 35° " 

12 ties 6 X 8 in. X 9 ft 432 " 

2 guard-rails 6 X 8 X 12* ft 100 " 

1050.00 B. M. 

And in the second case 

1 cap 12 X 12 in. X 14 ft 168 

(> stringers 6 X M i»- '^' ft 525 

12 ties 6 X 8 X 14 ft (>72 

2 guard-rails 6 X 8 X I2j ft 100 

146 5.00 

Or an excess of timber for each I2i ft. length, 415.00 B. M., 

equivalent to a waste of 175,300 ft. R M. per mile of trestle, 
at $26 per 1000 ft. B. M.= $4558 per mile. Practically but 
little increase of strength is gained. There is less danger of 



232 A PRACTICAL TREATISE ON FOUNDATIONS. 

a train wrecking the trestle or of tumbling off, which of course 
is an important consideration. Whether the additional safety 
secured is worth the expenditure of the above sum per mile 
might be a question ; but this can hardly be justified when 
framed trestles on the same road do not generally provide for it,, 
where it would seem that every precaution for safety should be 
provided, as the trestles are much higher, and consequently the 
destruction to life and property would be much greater should 
a train leave the track and be thrown from the trestle ; if con- 
siderations of safety control in one case they should control in 
all. It is evident that, in a 4-pile bent, with all piles vertical, 
the two piles under the rails have nearly if not all of the 
weight to carry, the outside piles only acting when the middle 
ones settle. For this reason some engineers use the 3-pile 
bents, the inner piles placed half-way between the rails ; the 
outer piles about \\ ft. from the rails on the outside. These are 
capped as usual, and the stringers placed between the piles and 
only one half the distance from the outside pile that they are 
from the middle pile. By this arrangement each outside pile 
bears two thirds of the weight on one rail, and the middle pile 
one third of the weight from each rail, or two thirds in all. All 
of the piles will bear an equal portion of the load. But the 
breadth of base Avill be reduced to 9^ to 10 ft. from outside to 
outside of pile, the bent, therefore, will be wanting in lateral 
stability. Moreover, as the weight is supported by the caps, at 
a point between the piles the caps will have a bending strain to 
bear, and though not requiring caps of greater dimensions than 
commonly used they will require a more frequent renewal to in- 
sure perfect safety. In this trestle the only saving is one pile for 
each bent, or each \2\ ft, or 424 piles to the mile ; assuming the 
average length of pile at 40 ft. we save 16,960 lineal ft. of piling 
at 30 cents a ft. = $5088. For low trestles there will be suffi- 
cient strength and stability. The caps are 12 ft. long, so there 
is saved also about 10,000 ft. B. M., to which may be added for 
saving in the length of the diagonal or X bracing some 5000 
ft. B. M., a total of 15,000 ft. at $26=$390, or a total saving 
of $5478 per mile. Some roads take advantage of this saving 



TIMBER PILES. 233 

and use the 3-pile bents, but the 4-pile bents are preferred and 
are more commonly used. 

If we are to use the 4-pile bent the piles should be driven 
so that they may all do full service not only in bearing the 
load, but in adding stiffness and strength to the structure ; or, in 
other words, all trestles should be built in such a manner as to 
make the most advantageous use of the parts composing them. 
This can be done by driving the outside piles on a batter of 3 
ins. per vertical foot, the same as that used for the batter-posts 
in framed trestles (the driver for such piles has already been 
alluded to). It costs no more than the 4-pile bent with all ver- 
tical piles; is as easily and as rapidly built. All of the piles 
carry a portion of the load ; the outside piles give stability and 
stiffness to the structure, when it becomes necessary to cut the 
piles off below water surface and to build frame trestles on 
them the piles are in the proper position to receive the weights 
to be carried — that is, in the prolongation of the posts of the 
trestle, both vertical and inclined. This is not the case in bents 
with vertical piles, and when these are cut off the batter-posts 
have no direct support under them unless extra piles are driven 
for the purpose, ultimately adding 848 piles per mile, or 2 to 
the bent. It would be equally sensible to construct the framed 
trestle bents with four vertical posts. This will probably be real- 
ized when contractors are forced to burn up their old, rickety 
and broken-down drivers that have been in use for a quarter of 
a century. In a 3-pile bent with outside batter-piles the piles at 
the top are arranged in regard to the rails, as in the vertical 
pile bent. But whatever may be the height of the trestle bent 
its base is spread proportionally, and its stability is secured. A 
trestle with 3-pile bents of this kind has more bearing power, 
more stability, and costs less by $5478 per mile than a 4-pile 
bent as usually driven with all vertical piles. Whether 4- or 
3-pile bents are used the outside batter piles should be used. 
These four types of trestle bents are shown in Figs. 5, 6, 7, 
and 8, Plate VI, respectively ; a mere glance at the drawings 
establishes the truth of the above comparisons. The X brace 
of 3-in. plank are used in all cases, and longitudinals should be 



234 A PRACTICAL TREATISE ON FOUNDATIONS. 

used when the trestles are over 10 or 12 ft. in height. The 
decks, composed of stringers, ties, and guard-rails, are or may- 
be the same in all cases. Figs. 9 and 10, Plate VI, show the 
elevation and plan for either type used. 

105. Sometimes it is necessary or desirable to use pile 
foundations either of wood or iron, from an economical point 
of view, when the bed of the stream is of a rocky material, as 
on coral reefs or layers of marl or other soft stone, into which 
it is either very difficult or impossible to drive piles with or 
without shoes. In such cases holes can be drilled of the 
proper size, a fraction less in diameter than the piles and to 
the required depth, and piles can then be driven firmly into 
these. The depth need not be very great, — from 1 to 3 ft., — as 
the only object is to hold the bottom of the pile in place, or 
small screw disks of iron can be fastened to the bottom of the 
pile, and by levers or other suitable machinery the piles can be 
screwed into the material to a sufficient depth. This would, 
however, be rather applicable to iron shafts or columns than to- 
wood. Upon these suitable platforms are constructed. Such 
structures are frequently constructed for various purposes on 
the sea-coast. It must be remembered that timber cannot be 
used in such situations unless creosoted, as it would soon be 
destroyed by sea-worms. 

106. Instead of drilling holes for piles, cribs heavily weighted 
with broken stone could be sunk on the bottom, and either 
timber or iron trestles could be built on these and well bolted 
to them. In this manner also trestles are sometimes built across 
rapid streams with rocky beds. A timber crib is framed, with 
pointed ends, 4 or 5 ft. wide, and somewhat longer than the 
bottom sill of a trestle bent, which for a trestle 20 ft. high 
would be about 24 or 25 ft. ; this is sunk in place until one end 
is on the rock, and then, while suspended in a horizontal posi- 
tion, broken stone is forced under and around until a uniform 
and solid bearing is secured, as described in sinking cribs for 
piers in rocky beds. The crib is then filled with broken stone, 
the trestle framed on the crib, and secured to it by iron straps. 
Plank can also be spiked to the posts of the trestle, and the 



COST OF TIMBER 'TRESTLES. 2$$ 

inclosed space filled with broken stone to add to its stability. 
Such trestles will stand a very great pressure in times of floods. 
The bents should be placed in a plane parallel to the direction 
of the current rather than perpendicular to the line of road. 

Article XLV. 
COST OF TIMBER TRESTLES. 

107. TIMBER trestles should only be regarded as temporary 
expedients, required by considerations of economy or rapidity 
of construction, or sometimes from necessity; and it is generally 
expected to replace them by earthen embankments, iron via- 
ducts or trestles, or by masonry abutments, piers, and bridge 
spans. Such considerations should not be allowed too much 
weight in designing and constructing such structures, as ex- 
perience proves that they often remain for many years, repaired 
and renewed from time to time ; often this is not done until 
some disastrous accident or wreck occurs, and even under favor- 
able circumstances the substitution is slow and gradual and 
many years elapse before it is entirely made. 

108. When framed trestles are to be built on the piles of 
former existing pile trestles, a record of the original pile-driving 
would be an important paper. Unfortunately, such records are 
not usually made, and if made not preserved. A pile trestle 
suitable to carry the comparatively light engines and loads of 
20 years ago might not be strong enough to carry those of the 
present day, unless the piles were originally driven to the 
depths and resistances previously mentioned as safe under the 
present heavy loads. The writer has generally kept a pile re- 
corder and inspector with every driver. The records showed the 
number of blows, the length of each pile, its larger and smaller 
diameter, and its penetration at»each blow for the last 4 or 5 
blows, and the depth driven in the soil, the number of feet cut 
off after driving, the extent of brooming or splitting if any ex- 
isted — in other words, a complete history of each pile. All that 
is needed is an honest young man, who will obey instructions. 
The satisfaction in such a record is worth all it costs ; it will 



236 A PRACTICAL TREATISE ON FOUNDATIONS. 

make known the weak points in a structure, and will enable the 
chief engineer to have a full knowledge of the character of the 
work done, and to order additional piles to be driven in certain 
places, if the record should seem to require it. Daily records 
of the progress of the work should be made and forwarded at 
stated intervals, with nature, causes, and extent of delay. This 
is applicable to all kinds of work, and at all times, requires but 
little extra labor on the part of resident engineers and inspect- 
ors ; makes these young men alert and observant, and keeps the 
chief engineer fully posted on matters of detail and importance, 
and in addition such records are of great value to the company 
for future reference and use. The want of such records often 
costs the company many thousands of dollars, while the cost of 
having them will amount to only a few hundred dollars. A 
striking case of this kind occurred in 1886-87, when the writer 
was chief engineer of the Mobile & Birmingham Railway. A 
railroad had been constructed for 60 miles out of Mobile to 
the Tombigbee River and was operated for several years, but 
owing to the inability of the company to renew the trestles the 
aggregate length of which was about 5 miles, the road had been 
abandoned for several years. This road was constructed in 1871— 
72. Upon assuming charge of the rebuilding it was naturally 
concluded to cut off the old piles below low-water line and to 
build framed trestles upon the old piles ; there were no records 
made, or certainly none were filed among the papers of the 
company that were preserved. This want of information caused 
some hesitation, but, believing that the road had been originally 
constructed in a thorough manner, a large force of hands was 
employed at several different, points to cut off the piles ; lengths 
of trestles were measured, bills of material made out, and par- 
tial contracts made. In the mean time, all of the old piles on 
several trestles had been cut off; considerable time and money 
had been spent on these, when unexpectedly the writer was 
called to examine the trestles at one or two points, and to his 
surprise he found that in many cases where an excavation had 
been made to get below the line of constant moisture the piles 
.had been entirely undermined at a depth not exceeding 3 or 4 



COST OF TIMBER TRESTLES. 2$? 

feet. Examinations were made at other points to fh id t'. le points 
of the piles, which was done without difficulty. It became nec- 
essary to change all plans and contracts, and to 1 epile the en- 
tire distance. Information obtained from old residents pcinted 
to the fact that originally no special inspection of the diiving 
had been made, and the contractors had been left to do very 
much as they pleased ; that if a pile was inconveniently long it 
would be cut in two pieces and hit a few blows, and that the 
trestles had been to a large extent built in this way. The 
business on this 60 miles was very small; only light trains 
drawn by light engines had been run over it, and these poor 
trestles were able to stand the small loads brought on them. 
After discovering this condition of things no confidence could 
be placed in the bearing of the piles in any of the trestles. 
To change orders at the mills, to make contracts for driving 
piles, and to change contractors, cost the company a good deal of 
money and loss of time, involved the company in suits ; and in 
some instances these were decided against the company, not- 
withstanding the fact that it had been provided in the contract 
that the right to change plans or reduce quantities of material 
was specifically reserved. Had a regular pile inspector been 
employed such work would not have been allowed, and the 
chief engineer would have been posted in regard to the matter. 
Had this road been completed in the beginning and heavy 
engines and trains run over it, many of the trestles would inev- 
itably have given way, and life and property would have been 
destroyed. 

One trestle on this road, about 1300 ft. long, was built 
with black cypress piles ; and although these piles were rather 
small, not averaging more than 9 or 10 ins. in diameter, had 
been exposed for more than 1 5 years, many of them were found 
in a fair state of preservation, and had been used continually 
for hauling logs to a saw-mill in the neighborhood — a small 
locomotive running over it constantly, drawing flat cars loaded 
with lumber. All of the pine timber originally used had en- 
tirely rotted and in the main fallen down, though in places 
some sound timber could be found. 

Some engineers do not cut off the piles and build framed 



238 A PRACTICAL TREATISE ON FOUNDATIONS. 

trestles, but repair and renew the trestles by driving new piles 
when necessary. 

109. A comparative estimate will now be given of the 
quantities and cost of framed trestles and pile trestles of the 
same height. We will assume a trestle, the total height of 
which is 21 ft. 9 ins., the framed trestle resting on mud sills, 
bents I2£ ft. from centre to centre ; we then have, for a length 
of i2£ ft: 

2 guard-rails 6X 8jns.Xi2£ft 100 ft. B. M. 

I2ties 6X 8 " X 9 " 432 " 

4 stringers 6 X 14 " X 12* " 35Q " 

1 cap 12 X 12 " X 10 " 120 " 

2 posts 12 X 12 " X 19 " 456 

2 batter-posts 12X12 " X 19I " 47i 

1 sill 12X12 " X 19* " 2 34" " 

6mud-sills 12X12 " X 5 " 360" 

2 diagonal braces 3 X 12 " X 26 " 156" 

2679 

Total timber in a length of I2§ ft. 2679 ft. B. M. at $26.00= 
$69.65. The timber in the pile trestle is the same as in the 
frame trestle diminished by the posts, bottom sill and mud-sills; 
or, in this case, 1158 ft. B. M. at $26.00 = $30.10, and increased 
by 4 piles 50 ft. long = 200 lineal ft. at 20 cts. per foot = $40.00, 
or the total for 12J ft. = $70.10, a difference of 50 cts. nearly in 
favor of the framed trestle. The cost of the iron is generally 
included in the price for framing, and is practically the same in 
both cases. In the first case the cost per foot of length is $5.57, 
and in the second $5.61. The above prices are the actual con- 
tract prices paid for about 5 miles of trestle in 1886. For tim- 
ber framed in trestles the price varies from $22.00 to $30.00 
per 1000 ft. B. M., whereas the cost of driving and furnishing 
piles varies from 20 to 40 cts. per lineal foot; and although in 
the example above given the cost of the two trestles are prac- 
tically the same, at different prices between the limits above 
given there might be a wide difference in the relative costs. 
In general, it can be stated that the cost of framing timber in 
trestles including the iron will be from $8.00 to $10.00 per 1000 
ft. B. M. ; and this added to the ascertained cost of the timber, 



COST OF TIMBER TRESTLES. 239 

delivered and piled at some convenient point near the site of the 
structure, will give a close approximation to the cost of the 
completed structure. And in the same way we may say that 
10 cts. added to the cost of piles per foot of length when de- 
livered at the site of the structure will be somewhere near the 
total cost per foot of piles when driven ; but this is more liable 
to variation than the cost of framing, as the handling of piles 
costs more in some cases than in others : if, for instance, piles 
can be delivered on the banks of a stream and then floated to 
the driver, the handling will cost but little ; if, on the contrary, 
they have to be dragged over swampy ground for any distance, 
or a track has to be laid and the piles hauled on trucks, the 
cost will be greatiy increased. The labor of cutting off piles 
to receive the caps is generally included in the cost of framing; 
and unless the same party does the driving and the framing, 
the party driving the piles will add something for the cutting 
off, and the party doing the framing will not make any deduc- 
tion on that account. And in either case the amount of work 
to be done in any one place materially affects the cost of the 
work, as camps have to be established, shanties constructed, 
supplies of provisions secured. Every move of camp, transfer 
of drivers, machinery and tools add to the cost of the work. 
The cost of the work, however, will be found within the limits 
above given— that is, for framed work from $22.00 to $30.00 
per 1000 ft. B. M., and from 20 to 40 cts. per lineal foot of 
piles driven; the superior limit also including the cost of cutting 
off piles under water. The weight of round iron for each foot 
of length is as follows : 

Diameters \ in. $ in. £ in. 1 in. 

Weight per foot 0.66 lb. i.oolb. 1.5 lbs. 2.64 lbs. 

" nuts and heads 0.20 " 0.36 " 0.7 " 1.75 " 

two-plate washers. .. .0.20 " 0.20 " 0.2 " 0.31 " 

Total weight 1.06 lb. 1.56 lbs. 2.4 lbs. 4.70 lbs. 

From this table it is easy to calculate the amount of iron and 
cost per bent and one span of 12^ ft. in length. Some engi- 
neers use a little heavier bolt than others, but the following 
will be ample for any trestle. Wrought spikes will weigh from 
i to f lbs. per spike 10 ins. long and £ in. square under head. 



240 A PRACTICAL TREATISE ON FOUNDATIONS. 

The bill of iron for a bent of trestle and one span of 12^ ft. 
in length will be as follows : 

6 bolts for fastening guard-rails to cross-tie, $ in. X i ft 3-9 6 lbs - 

Nuts, heads, and washers for the same . . . .• 2.40 

18 spikes fastening guard-rail to ties, ■& in. X 10 in 9.00 

24 " " ties to stringer, I in. X 10 in , 12.00 

2 bolts for fastening stringer to cap, f in. X 2' 4" 3-6o 

Nuts, heads and washers I -3o 

8 bolts for bolting stringers together, |- in. X i\ ft.' 12.00 

Nuts, heads, and washers 4-48 

12 bolts for fastening X-bracing to posts, cap and sill, $ X 1$ ft. .11.88 
Nuts, heads, and washers 4-So 

Total iron for each 12^ feet of trestle 55. 72 lbs. 

In case of pile trestle add 4 drift bolts, 1 in. X 2 ft 21.16 

And if longitudinal bracing is used, 4 bolts i in. X T i ft 3-9 6 " 

Or total iron 80. 84 lbs. 

If straps I in. X T i in- X 2 ft. are used instead of drift bolts, 
8 straps, 5 lbs. each = 40.00 lbs. 
16 bolts i in. X 15 in- = J 3- 12 " 
Nuts and heads = 3.20 " 

Total 56.32 lbs. less drift bolts 21.16 lbs. = 35.16 lbs. 

Total 116.00 lbs. 

In the three suppositions above, the amount of iron per foot 
of length of trestle is respectively 4.45 lbs., 6.47 lbs., 9.28 lbs., 
and the cost at 5 cts. per pound is respectively 22£ cts., 32^ cts., 
46I cts. These differences seem small, but they amount to a 
considerable sum in a mile of trestle. The second costs 
$532.40 more than the first, and the third costs $1325.12 more 
than the first, and $792.72 more than the second for each mile. 
It is often necessary to use the straps, notwithstanding the in- 
creased cost, and in addition when a trestle is to be renewed 
the straps can be used over again, whereas drift bolts can rare- 
ly be used a second time ; and for this reason straps, though 
more costly at first, will prove ultimately to be the most eco- 
nomical, and in addition lessen the labor and cost incident to 
repairs and renewals. Instead of using screw bolts for the 
longitudinal and diagonal braces, either wrought or cut 
spikes are frequently used ; ultimate economy will result by 
using the bolts, besides other advantages. This subject has 



COST OF TIMBER TRESTLES. 24I 

been discussed more in detail than it apparently deserves ; 
but the importance of such things is apparent to both engineer 
and contractor, and it will often be found that a little knowl- 
edge on these seemingly small and unimportant subjects will 
be of inestimable value to the engineer. Bolts are simply used 
as a rule without any regard to the actual diameters required — 
i-in. bolts used where a f-in. bolt would be sufficient, and f -in. 
bolts used where a -f or ^-in. bolt would answer every purpose. 
A glance at the foregoing table shows that f-in. bolt with head, 
nut, and washers weighs 2.4 lbs., whereas an inch bolt weighs 
with nut, head, and washer 4.7 lbs. for a bolt 1 ft. long, that is, 
about twice as much. 

1 10. When the bents are placed farther apart, or when the 
spans are longer, the number of bents to the mile are less, 
thereby saving material ; but the length of the stringers re- 
quired causes an increase in their dimensions or in their number 
or in the timber required in the straining-beams and struts, and 
some increase in the number of bolts. With any given height 
of trestle it would be an easy matter to determine the economi- 
cal length of span to use, as the dimensions of the timber in 
the bents themselves are practically the same in spans from \2\ 
ft. to 25 ft. in length. In the shorter spans there is always a 
large excess of timber in the bents above that actually required 
to carry safely the loads, as the four posts together have a total 
cross-section of at least 528 sq. in. area, or a safe resistance to 
crushing at 500 lbs. per sq. in. of 264,000 lbs., whereas the 
total load, rolling and fixed, would not exceed 90,000 lbs., and 
for the 25-ft. span the total load will not exceed 140,000 lbs.; 
therefore up to this limit, economy would justify the long spans 
rather than the short ones. But as the spans increase the sup- 
ports or foundations of the bents must be stronger, and in pile 
trestles more piles to the bents would be required, unless the 
material into which they are driven is firm and compact. En- 
gineers have apparently settled on certain lengths of spans 
without considering the question of economy, and we therefore 
find the standard spans for a single-story trestle either I2-| or 
14 ft., occasionally 15 ft, and for trestles of two or more stories 
20- and 25-ft. spans, the dimensions of stringers for the spar-, 



242 A PRACTICAL TREATISE ON FOUNDATIONS. 

seem to be determined in the same arbitrary way ; and we 
find for the spans 12 J, 14, 15 ft. the following dimensions re- 
spectively: 4 pieces each 6 X 14 ins., 7X15 ins., and 8 X 16 
ins. Applying the formula mWl = nfbJi 1 to these three cases, 
W being the equivalent centre load, or one half of the uniform 
load on the clear spans, I = 1 i|y 13, and 14 ft. respectively, and 
the load 6000 lbs. per ft. is equal to 8625, 9750, and 10,500 lbs. 
respectively ;/= ^, b = 6, 7 and 8 ins., and /= 138, 156 and 16S 
ins., respectively. We find /i=iy^ ins., 18 ins. when f= 1000 lbs., 
and 14 ins., 14I ins., and 15 ins. respectively, when/= 1500 lbs. 
We may then conclude that theoretically the assumed dimen- 
sions of the stringer are sufficient. For the spans 20 and 25 ft. 
the stringers can be of the same dimensions as given above ; 
the dimensions of the struts or rods used in bracing them being 
determined by the lengths of stringers supported directly by 
them, as explained in paragraphs 33 and 70. We will now de- 
termine by formula the depth of stringer required when six 
string-pieces are used instead of four, as above considered. In 
this the total load (one half of the total uniform load) divided 
by six will give the equivalent concentrated single load at 
the centre as illustrated in the following diagrams for the 
three different lengths of span. W then in the formula will 
34,500 39,000 42^000 equd respectively to 5m 6500j and 

7000 lbs., the value of all other quantities as above, from which 
the values of h or the depth of stringer in inches will be respec- 
tively (for/= 1000) 14 ins., 14I ins., 15 ins., and (for/= 1500 
lbs.) 11^ ins., 12 ins., 13 ins. Therefore we can use stringers 
under each rail composed of two pieces each 6 ins. X 14 ins., 7 ins. 
X 14! ins., 8 ins. X 1 5 ins., or three pieces 6 ins. X 1 ii ins., 7 ins. 
X 12 ins., 8 ins. X 13 ins. for the spans respectively of 12^-, 14, 
and 15 ft., centre to centre of bents with equivalent strength in 
each case, and either of these for the 20 and 25 ft. spans, when 
properly trussed as already explained. 

III. Shall we use then the standard 12^-ft. spans for a single- 
story trestle or 15-ft. spans? We have seen in paragraph 109 
that the cost of a 12-ft. span of framed trestle is $5.57 per foot 
.of length, and that the amount of timber was 2679 ft. B. M. in 



: 



COST OF TIMBER TRESTLES. 



243 



a span of 12^ ft. Deduct from this the guard- 
rails, cross-ties, and stringers, amounting to 882 ft. 
B. M. there remains 1797 — to which add 

4 stringers 8 in. X 15 in. X 15 ft. = . . 600 
15 cross-ties 6 in. X 8 in. X 9 ft. =. . 540 
2 guard-rails 6 in. X 8 in. X 15 ft. =. . 120 1260 

We have total timber in a span of 15 ft. in ft. B.M. . . 3057 

which at $26 per 1000 = $79.48, or cost per foot 
of length $5.30, a saving of 27 cts. per foot, equiva- 
lent to a saving of $1425.60 per mile of trestle. If 
six string pieces 8 ins. X 13 ins. X 15 ft. = 780 ft. 
B. M., or 180 ft. more timber, equal to $4.68 per 
span, or 31 cts. per foot, making the cost in that 
case $5.61 per foot, which shows that the substitu- 
tion of 8 X 1 3-in. stringers is not an economical use 
of stringers, as might have been expected ; but it 
may often be difficult to secure 8-in. X 15-in. string- 
ers of clear heart, whereas the 8-in. X 13-in. string- 
ers could be secured. But this is a little more 
•expensive than the spans of 12^ ft. long with 6-in. 
X 14-in. stringers ; and if this size of" stringer can 
be obtained it would be preferred, as there would 
be less pressure on the supporting material, whether 
mud-sills or piles. The above considerations and 
-principles have a very much more important appli- 
cation when deciding upon the economical rela- 
tions of piers and length of spans in long bridges, 
as in such cases the economical length of span is 
a matter of very great importance. But in this 
place it will be sufficient to say that as a general 
rule in low structures the spans should be short 
with many supports or piers, and in high structures 
the spans should be long and with few piers or 
supports. This will be considered more fully in a 
subsequent chapter. 

112. It may, however, be stated here that in 



^m 



244 A PRACTICAL TREATISE ON FOUNDATIONS. 

very high trestles it will be better to use spans from 40 to 50 ft. 
or more, and to construct piers or double bents similar to the 
timber piers described in paragraph 28. This can only be de- 
eided by a careful estimate of cost, including the extra precau- 
tions required to secure safe foundations. The principles in- 
volved have been fully discussed in the preceding paragraphs. 

113. As a general rule contracts provide for payments on 
the basis of so much per 1000 ft. B. M. framed trestles, and so 
much per lineal foot of piles driven, and sometimes in addition 
SO much per pound for iron used. Sometimes, however, the 
contract is so much per lineal foot of completed trestle. This 
last method possesses many advantages, as in this case there 
can be no dispute as to the final settlement. The work shows 
for itself ; either party can measure the length. In other cases 
questions may and do arise every month ; the contractor is not 
satisfied with his estimate, complaints are made, and extra bills 
presented. It is difficult to provide for every contingency in 
contracts — whether the lengths of posts mean from end to end 
of tenons, or whether the tenons are to be excluded ; how the 
cut-off ends of piles are to be paid for, and packing blocks 
between stringers ; excavations required for framed trestles 
resting on mud-sills, excavations for box-culverts, baling and 
pumping out water after rains, and many things that may arise 
during the construction of extensive works. It is true that 
these things can be provided for in the contract, but however 
fully and carefully the contract may be drawn such questions 
will arise, extra bills of innumerable kinds will be presented, 
and in the end suits will be brought which will often be decided 
in favor of the contractor, even when they have no shadow of 
a just claim. The contract based on the foot of length is open 
also to some objections, and particularly if the engineer does 
not know by careful estimates the relations between the costs 
of the actual quantities of material and the price per foot, as 
the contractor will certainly on his part put the cost per foot at 
the highest possible figure, making his estimates on very liberal 
allowances for quantities and contingencies. 

114. In order to avoid waste of material local customs should 



COST O* TIMBER TRESTLES 245 

be examined into. In large saw-mills doing a regular bus: 
certain definite lengths of lumber as well a z are in current 
demand, either for loeal use or for shipment to different and dis- 
tant places, logs are cul Oi ' yield these lengths and sizes ; and 
all bills of lumber that cannot be fully adjusted to these will 
entail either extra cost at the mills or waste in the works, for 
which the company will have to pay. If the common run of the 
square timber and plank, scantling, etc., is in lengths of even 
numbers, such as 12, 14, 16, 18, and 20 ft., it will be found 
economical to make the bill of lumber for any particular struc- 
ture to correspond as far as possible. To specify that the posts 
of a trestle bent should be exactly 18 ft. 3^ in. when an 18-ft. 
post would do as well is simply to add to the cost. Where 
definite lengths must be obtained it cannot be helped. Square 
timber such as 12 ins./ 12 ins. is used for stringers by some en- 
gineers, owing to the difficulty and cost of obtaining such sizes 
as 6X14 ins. or 7/ 15 ins. Either using shorter spans or using 
built beams for the longer ones, or as before mentioned the num- 
ber of piece- can be increased, thereby decreasing the depths 
to 12 inches. These matters are merely suggested as useful 
hints, and to suggest the advantages to be derived from allow- 
slight variations in designs, rather than to follow some 
stereotyped and iron-clad conditions simply because somebody 
else has followed them before — always bearing in mind that 
strength, suitableness, and durability are the first requirements ; 
but obtain these conditions at the least cost and in the least 
time. 

115. It is often necessary to cut piles off below water sur- 
face ; this may be required at any depth below the surface from 
3 to 20 ft. or more, as when cribs or open caissons are to 
be sunk until they rest on the piles. There are three methods 
of doing this, 1st. By the use of professional divers. This is 
an expensive and slow process, as at best they can work only a 
few hours a day, and they charge high for their services. The 
diver's suit consists of a water-tight canvas suit of clothes, 
which covers and fits the body from the neck to the ankles. 
Around the wrists and ankles this is bound tight to the skin by 



246 A PRACTICAL TREATISE ON FOUNDATIONS. 

strong rubber bands. Over his head a copper helmet is placed,, 
in which are thick glass plates called bull's-eyes ; this fits over 
his shoulders and is fastened to the water-proof suit by proper 
clamps, rubber bands being placed between. Connected with 
this helmet is a long, flexible tube or hose, which connects with 
the helmet at one end with a valve opening inward, and at the 
other with an air-pump. The helmet also has an escape valve 
for foul air opening outward. The bull's-eyes are protected by 
a metal netting to prevent danger of breaking ; these should have 
water-tight valves, which the driver can close if required. To 
enable him to sink in the water the soles of the shoes are made 
of lead, and in addition lead weights are fastened to his breast 
and back. There is an opening in the helmet, which is closed 
by screwing on a cap just as the driver is ready to descend.. 
The helmet is made of copper. As soon as the cap is adjusted 
the air-pump must be started, very slowly at first, but more 
rapidly as the diver descends. A tender, as he is called, holds 
the hose in one hand and a rope securely tied to the body of 
the diver in the other, and he pays out these as the diver de- 
scends or moves about on the bed of the river. It requires two 
men at the pump — one at work and the other resting ; these 
relieve each other at short intervals, and they should turn the 
crank at a uniform rate, so as to keep a constant pressure of air 
in the helmet. The diver signals by jerking the rope once, 
twice, or three times ; these have some understood meaning, 
such as more air, less air, or to lift him up, and so on. As he 
rises toward the surface the pump is worked slower and slower, 
and when the cap is removed it stops. Divers can work in 
depths of water to 75 or 80 ft., but only for a very short time 
at the greater depths. Owing to the cost of the diver's ser- 
vices piles are cut off by saws worked by machinery from 
above. 

116. A simple arrangement for this purpose is to fasten a 
cross-cut saw to the bottom of a frame which is connected to a 
rod suspended from a bolt attached to a frame constructed on 
a barge ; the saw being adjusted to the proper depth, a swinging 
motion is imparted to it by men on the barge or platforms from 



COST OF TIMBER TRESTLES. 2\J 

above, and as it enters the pile it is pressed forward by a lever at- 
tached to the bottom of the lower frame. When one pile is cut 
off, it is moved to the next, and so on. Where there is no great 
current, or no ebb and flow of the tide exists, good progress 
can be made and good work done by this method. While- 
sawing the boat must be kept level, unless the frame above 
admits of the suspending-rod sliding up and down. Where a 
large number of piles are to be sawed off, the following arrange- 
ment is used (see Fig. 2 A, Plate Vj. 

117. A frame is constructed on a barge, or, better, a floating 
pile driver. A long iron shaft carrying a horizontal circular 
saw is so suspended and connected in the leads that it can be 
turned and at the same time raised or lowered in the leads; a 
band wheel or drum is connected with the shaft ; the power 
band connects this with the drum of an engine. When the 
power is applied the shaft and saw are made to revolve rapidly. 
The saw is adjusted to the proper depth, and started ; the 
pile is cut off in a few seconds. If there is no strong cur- 
rent, any number of piles can be cut off in a very short time. 
The only difficulty in a current arises from the difficulty of 
holding the barge steady. This can be easily controlled. In 
a tidal stream the depth of the saw has to be changed more 
or less rapidly as the tide ebbs and flows. To regulate this an 
accurate tide-gauge must be placed in some protected place, 
where it can be easily observed either by the foreman on the 
barge or by an assistant ; a corresponding scale is also placed 
on the leads, adjusted to the plane of the top of the shaft, or 
some well-defined mark on the shaft. The reading on the 
scale and gauge are taken simultaneously at the commence- 
ment of the sawing, and afterward the saw is raised or lowered 
\ in., \ in., 1 in. from time to time as the tide falls or rises. With 
proper care and precaution a large number of piles can be 
cut off at practically the same elevation. Upon these the 
opon caisson, or crib, or other structure, can be lowered. See 
Fig. 1 A, Plate V. 

118. In driving piles over a space to be occupied by the 
structure, the outside piles should be driven so as to enclose a 



248 A PRACTICAL TREATISE ON FOUNDATIONS. 

space several feet larger than the actual base of the structure, 
or equal to that covered by the platform or bottom of the 
caisson, as explained in paragraphs 20 and 21, and shown in 
drawing Figs. 1 and 2, Plate IV. 

119. As a rule, a structure thus sunk on the piles simply 
rests on them, the weight holding it in place ; and although it is 
desirable to sink such a structure exactly in its true position, a 
few inches one way or another out of line or distance is not a 
matter of much moment in most cases, as the masonry required 
to sink it should be a few inches larger than actually required ; 
and when the structure is finally resting firm and true, an offset 
can be made on the top of the masonry so as to place the 
structure in its true line and distance. The little excess of 
masonry thus used is far less expensive than that of repeated 
raising and lowering the caisson. And unless strong staging 
is constructed around the caisson, and it is suspended and 
lowered by long rods with threads and nuts, it is almost im- 
practicable to lower a caisson absolutely in a desired position. 
Such staging and apparatus is expensive, the lowering is slow 
and tedious. If necessary, do these things; but when not 
necessary, such useless refinements will do to talk about, but 
must be paid for by somebody. Contractors will always make 
the company pay dearly for it. The driving of a few extra 
piles is far better and less costly, a small margin in the size of 
the platform being allowed. This is, in fact, necessitated by 
the requirements of its construction. 

120. Cases may arise where it becomes necessary to pre- 
vent any tendency to slide off of the piles. In such cases 
timber strips can be bolted to the bottom of the platform, 
projecting downward between and below the heads of the 
piles, which will hold the structure in place. And in some 
cases iron pipes £ or 1 in. in diameter are built in the caisson, 
extending through the bottom ; and when the caisson finally 
rests on the piles, long spikes or pointed drift-bolts can be 
dropped on the heads of the piles and driven into them by 
blows from above. But unless a grillage is constructed with 
small square openings in it, so as to guide and hold the piles in 



COST OF TIMBER TRESTLES. 249 

certain positions, the pipes would be as likely to miss the piles 
as to rest on them. Where such precautions are not neces- 
sary the exact positions of the piles are not of much moment ; 
but a reasonable effort should be made to drive them in rows 
at specified intervals, such as 2\ ft. from centre to centre, and 
no great error in position should be allowed. This cannot 
always be discovered until the piles are cut off, as when freed 
from wedges, bars, etc., they are apt to spring more or less. 

121. In driving piles for trestle-work, it is important that 
the piles in each bent should be in line with respect to each 
other, and also that the piles in the different bents should 
properly line up with each other, for appearance sake, if noth- 
ing else. The difficulty of driving piles in exact line is doubt- 
less very great and often impracticable, but it can be done 
much better than is often the case ; and the piles have to 
be sprung into position by the application of a great force. 
This necessarily bends the pile, or that portion of it above 
ground, thereby putting it in an unfavorable position to carry 
heavy vertical loads. Often they are so far out of position 
that they cannot be sprung or pried into position, and conse- 
quently the cap rests on only about one half of the pile. 
These conditions often result from inexcusable carelessness. 
Proper care is not taken to set the pile or to hold it in the be- 
ginning when it can be controlled, but after it has penetrated 
to a considerable distance in the soil, and out of plumb or 
position, desperate efforts are made to force it back, which 
will then be only partially successful, if at all, and doubt- 
less piles are seriously crippled or even broken below the 
ground in many cases. If the pile is properly pointed, head 
cut square, and set straight, and properly controlled by wedges 
or levers until it penetrates well into the surface, it will 
be easy to keep it straight to the finish. If a pointed pile 
strikes roots or even small bowlders or other narrow obstruc- 
tions, it will inevitably veer out of position, and no power can 
prevent it. It must be then put back the best possible, and in 
some instances new piles have to be driven. As previously 
mentioned, it is easier to keep a blunt pile straight than a 



250 A PRACTICAL TREATISE ON FOUNDATIONS. 

pointed one. In alluvial and the softer soils the pile should 
not be sharpened. It may sometimes be necessary, however^ 
in the firmer, stiffer soils. 

122. It would be better to mark with a peg or stake the 
position for the point of every pile ; this takes time and labor 
and the dragging and lifting of piles and heavy timbers will de- 
stroy many of them, but enough will remain to prevent any 
serious error in alignment or position. At any rate a peg 
should be driven to mark the centre of every bent, and for a 
few bents at the beginning and at intervals of every 200 or 
300 feet pegs should be placed for every pile. By this means, 
the piles can be lined by sighting, and the small and gradual 
errors can be rectified at short intervals, and by fastening 
battens at intervals on the piles already driven the leads of the 
driver can be properly lined for long distances. On shore,, 
with set lines of high stakes with strips of paper fastened to 
them, or better small flags, and occasionally placing the leads, 
in exact position with the transit, a true line can be kept for 
long distances. This should always be done when driving 
across water. 

123. It is better not to drop a pile after being lifted be- 
tween the leads, unless it is so long that this is necessary to 
get the head under the hammer, as it is difficult to drop it in 
the exact position or in a vertical line. Sometimes it is neces- 
sary owing to its length to drop it in front of the leads, so as 
to let it penetrate as far as possible into the soil, and then 
move the driver forward ; this requires great care. 

124. During the driving the direction of the pile is con- 
trolled by short blocks of wood, wedges, and levers. The leads 
of the drivers have iron brackets bolted to them, which hold 
the blocks of wood. The pile is lifted in the leads, lowered, 
and set in position at its point, forced into a vertical position, 
and the blocks are then placed in front and rear and wedged 1 
into position. This is done at one or two points in its height;: 
then the driving commences : the wedges are loosened or tight- 
ened so as to keep the pile vertical, or these are omitted, and 
the piles held and controlled by levers handled by the men_ 



EMBANKMENTS OF EARTH ON SWAMPS. I^Y 

This imposes very hard work on the men during the entire time 
of driving. Either plan can be used, but the first seems to be 
preferred. In stiff, compact silt, or ordinary clay it will be 
found convenient to drive a short pile, which is then pulled 
out, and the longer pile let down into the hole to a depth suf- 
ficient to bring the head of the pile under the hammer. Long, 
heavy piles can be set more accurately in this way than by 
dropping them in front of the leads. 



Article XLVI. 
EMBANKMENTS OF EARTH ON SWAMPS. 

125. As has been mentioned, timber trestles are to a large 
extent temporary structures, and it is expected to substitute 
iron trestles or embankments of earth sooner or later. This is 
also applicable to a considerable extent in building roads across 
extensive swamps ; but here it must not be lost sight of that 
the rises in the rivers and streams intersecting them, and the flow 
of the tides, especially in cases of storms, cover these swamps 
to the depth of 3 to 6 ft., and that ample water-way must be 
provided. Therefore long stretches of trestle are necessary,, 
which will constitute permanent important parts of the 
work. With this precaution it is intended to ultimately form 
earth embankments when material for the same can be secured 
in the necessary quantities and at a reasonable cost, and after 
the road has been constructed the construction trains can 
gradually dump dirt under and around the trestles until the 
embankments are completely formed. This will require a large 
amount of material, as the weight of the earth breaks through 
the matting or crust of roots and sinks to an unknown depth, 
but ultimately it will cease to settle, and a permanent embank- 
ment takes the place of the trestles. 

126. The matting of roots, of the cane and undergrowth 
that grow so largely in these swamps, has sufficient strength 
to carry the weight of two or three feet of earth and a light 
construction engine and dump-cars ; but this is its ultimate 



252 A PRACTICAL TREATISE ON FOUNDATIONS. 

strength. Any increase of weight will break through. When, 
therefore, earth can be obtained from the neighboring eleva- 
tions, these are staked out for borrow-pits, and tracks are 
laid from them to connect with the track of the main line 
of the road. The cross-ties are laid directly on the swamp. 
Trains loaded with earth are then run on to the main track, 
the dirt dumped on the swamp, and gangs of men raise the 
track with levers ; the earth is thrown and rammed under 
the ties. When this embankment reaches a height of two 
to three feet, the crust breaks short off along the foot of 
the embankment ; the embankment and track settle into the 
liquid mud underlying the crust. As fast as the material can 
be added it settles down; embankments several feet high in the 
evening will entirely disappear by the following morning, only 
to be filled again. This may continue for weeks, gradually 
settling more and more slowly, until finally it will practically 
cease, but in a greater or less degree will continue for months 
or years. 

127. The depth to which this will reach below the swamp 
is probably not known, but must be very great — not less than 
10 to 15 ft. This conclusion was reached by the writer in ob- 
serving the effect upon the swamp on either side of the em- 
bankment. The swamp bulges up fully 6 ft. on either side, 
somewhat abruptly facing the bank, and sloping rather gently 
from this summit outward to the level of the swamp, the 
crust forming over the mound a smooth, uniform covering, this 
mass of material representing the displacement made by the 
earth of the embankment. The earth doubtless assumes a 
slope considerably steeper than its natural slope, probably not 
more than \ to f to I, which would fully justify the depth 
above stated. After the lapse of time the mound settles down 
to the general level of the swamp ; this has been observed 
for miles. As a further proof of the great fluidity of the ma- 
terial and the depth to which the earth sinks, the effect upon 
the trestle approaches of bridges over the bayous and streams 
intersecting these swamps will be mentioned. The approaches 
to these bridges were built of pile trestles in lengths from 25 



EMBANKMENTS OF EARTH ON SWAMPS. 253, 

to 100 ft., and as the earth embankment was built up to the 
ends of these and pressed against the end piles, the entire 
trestle would be pushed forward, and this also pushing the 
abutments against the ends of the draw bridge so firmly as 
to prevent the draw from opening until the latch beams were 
moved backward ; and this was repeated many times. The 
material was so soft that in walking on the swamp and failing 
to plant the foot on the roots of the cane a man would sink to 
his waist before getting support. Such was the material upon 
which 14 miles of road was constructed, and into which piles 
driven from 30 to 40 feet would support load. The material 
for such banks should be sand and gravel or sand alone ; 
clayey soils would be apt to form mud, and be but little firmer 
than the swampy material itself. 

128. Sometimes a layer of long logs or plank is first laid 
on the swamp so as to give a broad base for the embankment, 
and if broad enough it would keep the crust on the surface 
from breaking through ; this answers well for support, but is 
probably wanting in steadiness, and a rapidly moving train 
tends to produce a wave-like motion. It is more economical 
than the first method, but cannot be considered as good or 
as safe. 

129. These methods of embanking are very objectionable, as 
the track has to be raised as the earth is packed under the ties. 
The result is that the rails are badly sprung or bent, both in a 
vertical and a horizontal plane ; the former being more objec- 
tionable than the latter, as the horizontal bends are the more 
easily seen and removed in part, if not entirely. A temporary 
trestle consisting of two short piles could be constructed of 
the proper height ; this would carry a light train, and the 
earth embankment could be formed under and around it. It 
would cost something, but at any rate would save the rails. 
It is the plan adopted even on firm ground, where the ma- 
terial is hauled out by engine and cars. The trestles in this 
case are framed and a light rail is used. The cost, however, 
would be the same in the two cases, which would be practically 



\J 



254 A PRACTICAL TREATISE ON FOUNDATIONS. 

offset by the extra labor required in rehandling the earth and 
raising the track. 

130. A few general remarks on earth-work will be made in 
this connection. The earth-work on a line of road consists of 
embankments and excavations. After locating the line of the 
road and establishing the grade line the road is divided into 
sections, somewhat in an arbitrary manner — the length of the 
sections being so regulated that the material excavated may be 
sufficient to make the embankments within the limits of the 
section, or for some other reason, the average length o.f the 
sections being from one to two miles. The earth from the 
excavation is hauled by barrows, carts, horse-cars, or by the use 
of a locomotive engine, depending on the amount of work, 
length of haul, etc. Sometimes it is more economical to waste 
the material from the excavation on the sides or at the ends of 
the cut, and to make the embankments from trenches, ditches, 
or borrow-pits along the embankment ; these matters are regu- 
lated by considerations that will not be discussed in this 
volume. Ditches along the embankments are necessary for 
purposes of drainage, and should be cut as straight and as 
regular as possible. A space called the berm should be left 
between the foot of the embankment and the ditch ; the width 
of this space is regulated so that the prolongation of the plane 
of the slope of the embankment shall pass well under the 
bottom of the ditch on the berm side, which will require a berm 
of from three to six feet, according to the depth of the ditch. 
The side of the ditch should have a slope whose base is equal 
at least to its depth, so as to prevent caving in. The cuts are 
excavated so that the slopes will be one vertical and one hori- 
zontal, or one to one as it is called, and the width at bottom 
varies for a single track from 16 to 18 ft., so as to allow 
for side drains. The width of the embankments on top vary 
from 12 to 14 ft., and the side slopes one and one half hori- 
zontal to one vertical. Whether the embankments are made 
from cuts or trenches, they should always be started with 
the full width required at the bottom and maintained the full 
width to the top. A too common practice is to make a narrow 



EMBANKMENTS OF EARTH ON SWAMPS. 255 

core at first, and then to widen it out by dumping loose earth 
on the sides ; the core being hauled over settles and compacts; 
the loose earth thrown on the sides sloughs off, and will not bond 
with it. And again, in making the filling a too common habit is 
to keep the embankment higher at the centre than at the sides. 
This is just the reverse of what it should be. Each layer should 
be a fraction lower in the centre. This rule should always be 
observed when the embankment is made in layers. Embank- 
ments made from cuts are generally built in one thick layer, of 
the required height of the fill; this is done by dumping the 
earth at the end of the embankment. The practice is still to 
keep the bank too narrow ; it should be built of the full width 
from bottom to top. Broken stone, gravel, sand, or mixed 
earths make the best embankments. Clay makes a good em- 
bankment when put up dry and properly drained. All earth 
embankments will settle more or less, depending upon the 
character of the material used, and the manner in which the 
embankment is constructed. Clay and ordinary earth settle s 
slowly, and to a considerable extent, and more than sand or 
gravel. It is not unusual to allow as much as ten per cent for ^ 
settlement ; that is, a bank ten feet high must be made eleven 
feet high on first construction. Low embankments that are 
made either by throwing the material from trenches, or by the 
use of barrows will require the full allowance for settlement. 
High embankments constructed by the use of scoops or drags 
drawn by horses, by horse-carts, and by engines and dump-cars, 
owing both to the time required in the construction, and also 
to the constant tramping and hauling over them, will settle to 
a large extent during construction, and will require but a small 
per cent, of additional height. The slopes of the cuts are liable 
to be washed into gulleys, and undermined by the flow of sur- 
face water running down the slope, or sinking into the soil and 
escaping along seams or through porous layers of sand or 
gravel. This can be greatly reduced by cutting surface drains 
on the up-hill side of the cut, or by surface drains on the slope 
made of timber, or by terra-cotta pipes imbedded in the slope, 
and emptying in the side drains at the bottom. Sodding the 



256 A PRACTICAL TREATISE ON FOUNDATIONS. 

slopes or sowing grass-seed on them is also a remedy for this 
trouble, besides adding greatly to the appearance. In some 
cases these methods fail, and the slopes will cave in. In this 
case benches can be cut at different elevations, so as to break 
the slope ; drains made on the benches will carry off the water. 
Foot walls can be constructed of masonry at the bottom of the 
slope ; even when very thick they often prove of little value. 
All of these means failing, the material can only be removed as 
it falls. If the weight and amount of traffic were the same in 
both directions a straight and level line would be desirable; 
but in the direction of the heaviest traffic gentle inclines or 
grades are advantageous, as they aid in hauling long and heavy 
trains, and are of no serious obstruction on the return with the 
lightly loaded or empty cars. Grades also facilitate the drain- 
age of the road-bed. Grades vary from o to 2 ft. per 100 ft. ; 
the usual grades, however, vary from 20 to 52.8 ft. per mile; 
they should not be used on curves, trestles or bridges when 
not absolutely necessary. 

131. The roadbed completed, when it can be economically 
done, on it should be placed the ballast, which consists of a 
layer of gravel or broken stone from 6 to 9 inches thick, upon 
which the cross-ties are laid ; then between the cross-ties 
gravel or broken stone should be packed. The ballast gives 
firmness to the bed and serves also to drain off the water, 
thereby keeping the track dry, and consequently preserving 
the ties. As a rule, however, the ties are first laid on the 
earthen embankment, the rails laid, and the ballasting done 
afterward, when it can be hauled in construction trains and 
distributed more economically. The track is raised, and the 
ballast then rammed under the ties and between them, as be- 
fore. When broken stone is used the ballast is built up to the 
top of the tie for its full length, with the proper slope on the 
sides. Sand and gravel also make good ballast ; but sand, espe- 
cially if very fine, makes a dusty road, and the grit deposits in 
the machinery, which causes friction and wear. Sandstone is 
apt to be pulverized, and has the objection just mentioned. 
In many sections of the country broken stone of any kind is 



EMBANKMENTS OF EARTH ON SWAMPS. 2$? 

hard to obtain, and the dirt ballast, so called, is used This 
simply means packing the dirt under and between the ties, so 
as to give firmness to the track. In this case drainage is pro- 
vided by simply sloping the top, so that the surface at the 
centre of the track is level with the top of the tie and slopes 
gently on each side, so as to fall to the level of the bottom of 
the ties at their ends. The water is thereby drained off. But 
this kind of ballast is apt to work into the condition of mud 
during very wet weather by the churning motion imparted to 
the ties by a rapidly moving train. But it is the only kind of 
ballast used on thousands of miles of road in the Southern and 
Western States. It is not favorable for very heavy loads or 
very high speeds. 

132. Cross-ties are placed generally at intervals of 2 to 2\ 
ft. centres; requiring from 2640 to 21 12 ties to the mile. The 
depth of the tie is from 6 to 7 ins., the width from 8 to 10 
ins., and length from 8 to 9 ft., 8| ft. being about the average. 
These ties are hewn on two sides and the bark stripped off 
the other two. It is usual to place the ties somewhat closer 
together at the joints, these being between the ties form the 
suspended joint. In the other case the joint rests on the tie, 
a broad cross-tie being selected for this. 

Cross-ties are generally made of white oak, post and chest- 
nut oak, white or yellow pine, and sometimes of other woods. 

133. The cost of the earth work varies somewhat, but, as a 
rule, the established price is : Earth, 20 cts. ; hardpan, 30 to 35 
cts. ; soft or loose rock, 40 cts., and hard rock in large masses, 
80 cts. per cubic yard, and when the material has to be hauled 
more than a certain specified distance an extra allowance is 
made, such as | or 1 cent per cubic yard for each hundred feet 
of haul over 300 or 500 ft. Disputes often arise on this point 
on the final settlement from the indefinite manner in which 
this is expressed in the contract. 

134. Cross-ties vary in cost from 20 to 50 cts. apiece, 
depending upon whether pine or oak is used, and upon the 
more or less abundance of the timber suitable for ties along 
the line of the road. These maybe taken as extremes, the 



258 A PRACTICAL TREATISE ON FOUNDATIONS. 

average prices, delivered and piled at Intervals along the road, 
being 30 and 40 cts. respectively. Piles of ties should be 
formed by first laying two or three ties with intervals on the 
ground, then a solid layer at right angles to these, then a layer 
of two or three, and another solid layer, and so on to the 
height of a man's head. This mode of piling enables the ties 
to be easily inspected, favors the gradual seasoning of the tie, 
and adds greatly to the life of the tie. Solid or irregular piles 
of ties cannot be properly inspected. The general rule is to 
require the ties to be hewn to smooth surfaces on top and bot- 
tom. Careless work leaves gashes in the tie that admit and 
hold water, thereby hastening rot. One end of the tie is 
required to be cut square, though the other may not be. The 
ties are laid with the square ends on a line parallel to the centre 
line of the road. 

135. On a road in Central America the writer used lignum 
vitse and mahogany ties. This is mentioned more as an illus- 
tration of the use of that particular kind of material, which 
grows, regardless of its intrinsic value, in any particular lo- 
cality, and which is often carried to the opposite extreme by 
using very inferior materials on account of the convenience 
and cheapness of obtaining them. Lignum vitse would doubt- 
less be an economical tie in the end, no matter what its first 
cost, but it cannot be obtained in large quantities. The life 
of a tie depends greatly on the use of good ballast and also 
upon its resistance to being cut into by the rail, as this induces 
rot and loosens the hold of the spike. This peculiar property 
is marked in the ties of the lignum vitae kind. 

136. As has been mentioned, the two proper and usual 
methods of building across swamps are first to dump the earth 
directly on the swamp, and continue doing so until settling prac- 
tically ceases, or to prevent settling by floating platforms of 
plank, fascine-mattresses, or logs ; and secondly, to drive piles 
and fill in to a great or less extent subsequently with earth. 
Either of these plans is good, but there have been fatal and 
serious blunders in building across swamps, by cutting canals 
&vith dredges along the road-bed and emptying the material on 



EMBANKMENTS OF EARTH ON SWAMPS. 259 

the road-bed. This is bad practice, for several reasons, 1. It 
cuts or breaks the crust formed by the matting of roots, which 
is the main reliance to prevent excessive settling and sinking 
of the bank. This has been done, and to remedy the blunder 
double rows of piles have been driven along the foot of the 
slope to hold the bank, but this failed — as this swampy mate- 
rial, especially when the crust is broken, has but little stability 
so far as lateral resistance is concerned, and the piles would 
spread outward at and near the top. The writer saw the 
above conditions on the road between New Orleans and 
Mobile. The subsequent labor and cost of securing a firm 
road-bed must have been enormous. 

2. The material of the swamp, even if it can be held in 
place, is in the writer's opinion, unfit for use in an embank- 
ment. There is now being constructed a road-bed across these 
same swamps, in which an attempt is being made to do away 
with the first difficulty by cutting the canal at a distance of 
50 to 1 50 feet from the road-bed. Whether this will be effect- 
ive and fully remove the difficulty, probably is yet to be de- 
termined. The material thus dredged is hauled and used in 
the embankment ; the second difficulty then still exists, and it 
is doubtful whether such an embankment will ever prove 
satisfactory. It is probable that a temporary trestle, built 
with two pile bents, and subsequently filled in with some more 
stable material, such as sand or gravel, would prove ultimately 
more economical and satisfactory. The method is certainly 
an improvement as compared with the preceding one just 
described. 

An interesting instance of this subject is the observed set- 
tling of the peaty soil in Holland. An embankment of sand 
8 ft. high, giving a load at base of 800 lbs. per square foot, 1/ 
compressed the peat underneath to two thirds its bulk ; final 
condition of stability was only attained after two years. The 
embankment afterward carried safely the railroad trains. The 
soil was covered with a fascine-mattresses, to distribute the pres- 
sure and prevent the sand sinking into the soft silt. In con- 
structing a station yard, a trench 15 ft. wide and 15 ft. deep 



26o 



A PRACTICAL TREATISE ON FOUNDATIONS. 



^ 



was excavated around the space and filled with sand, and a 
3-ft. layer of sand spread over the entire space ; and for the 
station building itself a pit, 15 ft. deep and of horizontal di- 
mensions each way 20 ft. greater than that of the structure, 
was excavated and filled with sand ; the sand, as has been 
mentioned, distributing the pressure over the entire surface of 
the excavation. 

The theoretical discussion of the stability of earth under 
pressure as found in Rankine is very pretty, even if not true, 
and easily reduces to the well-settled theory of fluid pressure. 
In Fig. 6, ABCD is the cross-section of the excavation in the 





Fig. 6. 



soft material, and AEFBDCA is a cross-section of the pro- 
posed embankment or other structure to be built. Making 
GE = h, GC = h' , <p' = angle of repose of soft material, w' = 
weight of one cubic foot of the soft material, w = weight of a 
cubic foot of the sand, gravel, or stone used in the structure, 

1 — sin <p' 
k' — — ■ — : — -77. Then GC, the depth to which the pit is to 
1 -f- sin r v 

be excavated, = h' = 



hwk' 



formula becomes, since k' =1, 



for a fluid <p' = o, and the 



k' = 



hw 



w —w 



or w (h -f- h') — w'k ', 



which simply means that the structure will sink until the 
weight of the displaced soil is equal to the weight of the struct- 



EMBANKMENTS OF EARTH ON SWAMPS. 26l 

ure itself, which is the law of fluid pressure ; for semifluids or 
firmer earths this is modified by the value of <j>' ', the angle of 
repose of the material. Such formulae should be of course 
used with precaution and a large factor of safety, and can 
only be regarded, as was mentioned in discussing the subject 
of retaining walls, as a very ingenious and masterly extension 
of the theory of fluid pressure to that of earth pressure. 

Those cases in which a firm stratum is underlaid by a soft 
material, such as mud or quicksand, involving as they do many 
difficulties and requiring special methods of construction, will 
be classed under the head of difficult foundations, and will be 
discussed in the next part of this volume. And similarly, 
where the soft material overlies a firmer stratum, where piles 
are not used, although there are but few such cases in which 
piles would not answer every purpose, and in general be 
economical ; but often they would be unsuitable, expensive, 
and undesirable. 



PART THIRD. 



Article XLVII. 
FOUNDATIONS— (CONTINUED). 

DEEP FOUNDATIONS. 

I. HAVING considered what may be called ordinary founda- 
tions, including timber trestles and pile trestles, and in part 
first masonry and masonry piers from the foundation-beds 
to the bridge seats, we will now explain and discuss those 
foundations requiring more costly and difficult methods of con- 
struction. For convenience, foundations were divided into two 
parts, that portion from the foundation-bed reaching to or nearly 
to the surface of the ground, and that portion above and extend- 
ing to the bottom of the superstructure ; these together are 
commonly known as the substructure. To complete this por- 
tion of the subject, it only remains to describe certain unusual 
methods of reaching the foundation-bed, where great depths 
below the water or earth surfaces have to be reached. These 
methods, disregarding the materials used, which may be either 
wood or iron or both combined, may be divided into two classes, 
ist. Where the desired depth is reached by simply dredging the 
material from the interior of a large timber or iron box or 
cylinder, suitably and strongly constructed for the purpose,, 
and forcing the structure to sink against the exterior friction 
on its sides, by sufficient weights or loads superimposed. 
Structures of this class are called either open caissons, or more 
commonly cribs. 2d. Those methods in which timber or iron 
boxes or cylinders are constructed with one or more air-tight 
compartments, except that they are open at the bottom. 

262 



THE OPEN CRIB. 263 

This part of the structure is called a pneumatic caisson, and 
upon this can either be constructed cribs of a greater or less 
height, on which the masonry rests, or this latter may rest 
directly upon the roof or deck of the caisson. 

2. The first or crib method will now be considered. When 
constructed of timber, the crib is composed of four double 
walls of timber, enclosing a space of the proper horizontal and 
vertical dimensions; the two walls of each side maybe built 
solid and connected together by horizontal struts and ties, or 
they may be built somewhat open and similarly connected. 
These walls near the bottom, and for a varying height, are con- 
structed with V-shaped sections, coming together at the bot- 
tom edge, thereby forming a cutting edge, and opening out 
gradually to a width of 8 or 10 ft., at a height of about 8 or 
10 ft. The outer wall has a batter or slope outward and 
downward, varying from a few inches to several feet, the 
inner wall is constructed to a slope of 45 or less. This 
lower section of the crib may be built solid with large timbers, 
or it may only be strongly braced with cross-timbers. Upon 
the top of this bottom section the two walls are built up verti- 
cally and parallel, or the outer wall may have a slight batter 
of about one half inch to the vertical foot, and the two prop- 
erly tied together. The object of the space between the two 
walls is to give strength and stiffness to the sides of the crib 
and at the same time to supply sufficient space for the weight 
required to sink the crib, which weight is generally either 
gravel, broken stone, or concrete. For cribs enclosing small 
areas the outer walls thus filled are all that are necessary. In 
large cribs, however, cross-partitions, similar to the enclosing 
walls, are constructed. One longitudinal partition will ordi- 
narily be sufficient, but there may be several transverse parti- 
tions. This construction divides the enclosed space into 
several square or rectangular divisions, open top and bottom. 
See Plate XI, Figs. I, 2, 3, and 4. 

3. A sufficient height of crib being built, either floating or 
on land and then launched, the crib is then floated and anchored 
over the proposed site of the pier and held in position by clusters 



264. A PRACTICAL TREATISE ON FOUNDATIONS. 

of piles, anchors, etc. The building is continued until the crib 
rests on the bed of the river or sinks some distance into it. 
Then the work of removing the material on the interior is 
commenced. Many more or less crude means of doing this 
have been practiced, such as ordinary scoops or iron buckets, 
connected to and worked by suitable gearing and machinery 
on top of the crib itself, or resting on platforms or barges. 
"But now some form of clam-shell dredge is generally used. 
This may be defined as a large bucket, composed of several 
sections so hinged and connected that when it descends the 
sections separate, and its weight forces itself into the soil or 
around and over bowlders; when lifted, the segments close 
together on the material, which is then lifted to the surface 
and either emptied into the river or, when necessary, into 
barges. While the material is being dredged out the crib is 
built up, the pockets filled with the stone or concrete. With 
the relief from resistance on the interior and the weight of 
the structure, the crib sinks into the material at the bottom, 
either gradually and continuously or at intervals, depending 
on the resistance and weight. The method is simple and was 
formerly resorted to for great depths, either where it was not 
desired to drive piles or where the ordinary coffer dams were 
either unfit or too costly. For depths, say from 30 to ioo feet, 
the pneumatic process has, of late, been largely substituted ; 
but the crib has been used where the amount of work would 
not justify the necessary first cost of the pneumatic plant or, 
for the same cause, it would be more expensive. Of late, 
however, in a few instances foundation beds at a greater 
depth than 100 feet below the surface have been required. As 
this depth is generally considered the limit of the pneumatic 
process, builders have resorted again to the use of the crib, 
either constructed of timber or iron, and to the iron cylinder. 
Three examples of this method will be briefly described. 

4. The design of a timber crib suitable for the above 
described purposes is fully shown in Plate XL Fig. 2 shows a 
plan or horizontal section ; Fig. I shows a cross-section and 
part elevation ; Figs. 3 and 4, Plate XII, show other details, etc. 



THE OPEN CRIB. 26$ 

This is a good example of the general construction of a crib, 
although it was in part designed for a combined crib and 
pneumatic caisson. It will be more fully explained farther on. 
5. One of the longest and largest structures in which the 
open-crib method was used in the foundations is the Pough- 
keepsie Bridge across the Hudson River, New York, full de- 
scriptions and illustrations of which can be found in the Engi- 
neering News and the Engineering and Mining Journal. The 
following are the principal points of interest : There were two 
cantilever spans of 548 ft., and two counter balance or anchor- 
age arms of 201 ft. each, one cantilever span 546 ft., and two 
contiguous through trusses of 525 ft. — giving a total length be- 
tween end piers of 3094 ft., and including viaduct approaches 
6767 ft. The grade on the approaches was 66 ft. per mile ; 
clear height of structure above high-water 130 ft., making base 
of rails, as deck spans were used, 212 ft. above high-water. 
All masonry was of first class for facing stones, the backing 
being of concrete with large stones imbedded, so as to tie the 
face and backing thoroughly through the entire pier, as has 
been described under the head of masonry. The masonry 
rested on the cribs at about 10 ft. below high-water, and was 
built to about 30 ft. above high-water ; on top of the masonry 
steel towers about 100 ft. high were erected, upon which the 
superstructure rested. To a depth of 100 ft. or more below 
high-water, the bed of the river was composed of silt, clay, and 
sand, underlaid by layers of a firm, coarse gravel, between 
which and the rock, which was about 140 ft. below high-water, 
there was found a bed of compact gravel, upon which the 
structure finally rested at a depth of about 135 ft. below low- 
water. There were 4 cribs of the same general design and di- 
mensions. Bottom dimensions 60 X 100 ft., height 104 ft. ; the 
dimensions decreased somewhat toward the top, giving a regu- 
lar batter; they were built in the main of 12 X 12 in. hemlock, 
except the timbers which formed the cutting edges ; these were 
of white oak. The lower section of the crib of about 20 ft. in 
height was built of the usual V-shaped section of solid timbers 
for the outside and cross-walls, similar to the lower part of crib 



266 A PRACTICAL TREATISE ON FOUNDATIONS. 

shown in Plate XI. There was, however, only one cross-wall. 
The annexed diagram, Fig. 7, shows horizontal section at bot- 
tom of cutting edge (see dotted lines), and also at a point 20 ft. 
above, as seen by the full lines. C, C, C shows the cutting 
edges of the outside and middle walls ; B, B, B cross-bulk- 
heads 2 ft. thick' dividing the enclosed space into 14 cells or 
pockets, open bottom and top and extending from bottom to 
top of crib. These are the dredging chambers or compartments. 
The width of the cutting edges was only a few inches, and 
these walls then increased in the height of 20 ft. to 10 ft. on 
the sides, 9 ft. on the ends, and 16 ft. in the middle walls; these 
are shown by the shaded rectangles. Upon these solid walls 
the double walls of the crib above was built which formed the 
cells or pockets for the concrete filling. It is seen that the 
dredging chambers B, B, B, are for the 4 end ones 19 X 30 ft. 
= 570 sq. ft. at the plane of the cutting edge, and the inter- 
mediate ones are 10 X 30 ft. = 300 sq. ft. ; whereas at 20 ft. 
above in the plane of the shaded portions all chambers are 
10 X 12 ft. = 120 sq. ft., and continue this size to the top 
of the crib. Such cribs are built either partly on shore and 
then launched or entirely while floating ; when a sufficient 
height is built to reach from the bed of the river to a point 
somewhat above water surface they are floated into position 
and held by anchors, or clusters of piles, or by cribs loaded 
with stone and sunk at convenient points. The building of 
the walls of the crib, the weighting of the caisson with concrete, 
gravel, or broken stone is then proceeded with. The material, 
is dredged from the bottom through the open chambers 
B, B, B, and as the material is removed and frictional 
resistance decreases, the crib settles into the soil. In this 
structure the weight supplied was gravel, and afterward this 
gravel was removed, as I understand the description, and then 
these same pockets filled with concrete, as was also the dredging 
chambers B. The settling of the caisson was somewhat un- 
certain and irregular, dropping sometimes as much as 10 ft. at 
once. This uncertain and irregular settling is one of the diffi- 
culties attending this open-crib method. Under ordinary cir- 



THE OPEN CRIB. 



267 




268 A PRACTICAL TREATISE ON EOUNDATIONS. 

cumstances with the walls of the pockets well calked ; there 
should be no difficulty in using concrete for the weight, and 
thereby saving the time and cost of first filling them with 
gravel or stone and subsequently removing the same. At 
least such is the writer's experience in cribs 40 or more feet in 
height, even though some of the pockets were often left unfilled 
to the depth of 15 or 20 ft. below the water surface. A suffi- 
cient margin on the height of the crib should always be pro- 
vided to keep its top above water, and but little pumping 
should be necessary to keep the pockets free of water. Much 
of this concreting must have been done under water, which 
certainly is to be avoided if practicable. If such pockets had 
to be filled' first with gravel or broken stone, which is then 
removed and replaced with concrete under water, it would 
have probably resulted in as good a job, if pipes a few inches in 
diameter with a series of holes at different levels had been built 
in the gravel or broken stones at intervals, and instead of remov- 
ing the material, to have poured a grout made of cement alone, 
or at most with 1 cement and 1 sand, into these pipes, the head 
would force it through the holes and out between the gravel 
or stone, thereby more or less perfectly filling all interstices, 
and doubtless making as good a concrete as that ordinarily re- 
sulting from concreting under water. A somewhat similar plan 
has been tried, not on such an important and extensive work, 
perhaps, but is said to have given good results. The above 
described structure is specially noted for the size and height of 
the cribs and the depth of 135 ft. sunk below high-water. 
Although in many details the design and construction of 
these cribs may be different, yet the figures of Plate XI 
considered as a crib alone, without the shafts, pipes and 
horizontal partitions or roofs of the separate chambers, will 
represent a good design of all forms of open cribs; hence more 
elaborate drawings showing in details the cribs of the Pough- 
keepsie piers are omitted, and for these the reader is referred 
to the magazines mentioned. 

6. Another bridge of great length and involving many 
difficulties, in which the open-crib method was used, was 



THE OPEN CRIB. 269 

recently constructed by the Union Bridge Co., of New 
York, and known as the Hawkesbury Bridge, in New South 
Wales. In this case the cribs were constructed entirely of 
iron ; the horizontal sections of the crib were rectangular 
with rounded ends, spreading out from a point about twenty 
feet above the bottom. Except in regard to the shape of 
the cribs, the number of dredging tubes or cylinders, and the 
thickness and the strength of the plates, angle-irons, etc., the 
elevation given for the crib of the Diamond Shoals Light- 
house, designed by Messrs. Anderson & Barr, will be ample 
without further drawings to represent this particular case. 
And as Plate XI has been taken as a fair type for the con- 
struction of all timber cribs, so may the figures in Plate X be 
taken as a fair type of the all-iron cribs. Before givino- some 
of the details of the Hawkesbury Bridge a few remarks on the 
general construction of iron cribs will not be out of place. By 
referring to Plate X it will be seen that the lower section of 
the crib flares outward at a considerable angle ; this has doubt- 
less been characteristic of iron cribs, whereas in Plate XI the 
batter or outward flare is very slight, and the same may be 
seen in the plates showing pneumatic caissons. In either case 
the object is twofold. First, it increases the area of the base, 
thereby reducing the unit pressure on the foundation-bed ; and, 
secondly, is supposed to facilitate the sinking of the caisson or 
crib by reducing the friction on the exposed surfaces. So far 
as the first consideration is concerned, the bottom could be 
made of the required area, this continued for a certain height, 
and the area reduced abruptly to the size required for the 
structure above ; this, then, has no material importance. As 
to the batter facilitating the sinking it has generally been 
considered as absolutely necessary to have some batter ; 
the amount, however, has been different in different designs. 
Mr. Anderson, who has had great experience in sinking deep 
cribs and cylinders, expresses the opinion that in running 
sand and silt it makes but little difference whether they have 
any batter or not ; but if the material is tenacious, as in clay 
and compact silt, that a vertical surface on the outside of the 



2JO A PRACTICAL TREATISE ON FOUNDATIONS. 

lower section is to be preferred, as the material will not other- 
wise close in on the sides of the caisson, and that it would be 
more difficult to guide and hold the structure in a proper posi- 
tion. To confirm his view he states that both plans were tried 
in the Hawkesbury foundations, and all of the trouble occurred 
with the inclined sides, and little or none with those cribs that 
had vertical sides. The following table gives the depths sunk 
and total heights. The tops of the piers were 42 feet above low- 
water ; difference between high and low water, about 5 feet. 





Depth from 

Low-water to 

River Bed. 


Depth 

Below River 

Bed. 


Total Height from 

Bottom to Top 

of Pier. 


No. 1 


33 ft. 


55 ft- 8 in. 


135 ft- 8 in. 


" 2 


40 " 


108 " I " 


190 " 1 " 


" 3 


43 " 


96 " " 


181 " " 


" 4 


21 " 


118 " 6 " 


181 " 6 " 


5 


19*" 


117 " 5 " 


178 " II " 


6 


47 " 


108 " " 


197 " 



Some difficulties were encountered, as would have been an- 
ticipated in a structure of such magnitude. 

The spans were constructed on false work erected on very- 
large barges, and floated in between, and then lowered on the 
piers. 

The length of this bridge was 2896 ft. in length. The depth 
to be sunk was as shown in the above table, through water, 
mud, and sand, finally resting on a bed of compact gravel. 
Such were the general dimensions, requirements, and results. 
In 1884 invitations were extended to the bridge builders in 
many parts of the world. The builders were to submit their 
own plans, both for the substructure and the superstructure, 
subject to certain limitations as to dimensions and strength of 
materials. A large number of plans were submitted by Eng- 
lish, French, and American builders, which resulted in the 
contract being awarded to the Union Bridge Co., of New York, 
for the gross sum of about $1,835,000. No official or full par- 
ticulars of this structure have been published by the builders. 
The following general facts, to which have been added some 
calculations of weights, resistances, etc., by the writer, are 
taken from the columns of the Engineering News. The total 



THE 01' EX CRIB. 21 \ 

length was divided into five spans 416 ft. long each, and two 
spans each 408 ft. long, by six piers and two abutments. As 
the depth to be sunk far exceeded the generally accepted limit 
of the pneumatic process, it was determined to use the open- 
crib method. The crib was constructed entirely of iron. Except 
that the enclosing walls were composed of iron plates stiffened 
by angle-irons and strong iron braces between the double walls, 
the general design was the same as in timber cribs. The iron 
plates of the outside and partition walls were -| in. thick, the 
necessary weight to sink the crib being deposited between 
walls. These walls enclosed three tubes or cylinders 8 ft. in 
diameter ; these extended to about 20 ft. from the bottom, at 
which point they commenced to swell out in a bell or funnel 
shaped mouth to the bottom edge, forming with the outside 
and partition walls strongly built and connected cutting edges. 
The horizontal sections were rectangular with rounded ends, 
the dimensions of the bottom section being 52 X 24 ft.; these 
dimensions gradually decreasing upward, so that at a point 
twenty feet from the bottom the cross-section was reduced to 
48 X 20 ft., and thence continued at these dimensions for a height 
of about 155 ft. to low- water. This was built up in sections of 
about 5 ft. as the dredging and sinking progressed. The tubes 
were connected with the side and partition walls by strong iron 
braces. The entire open space around the tubes was filled with 
concrete as the sinking progressed ; this, with the weight of 
iron, overcame the resistance. The material was dredged out 
through the tubes by means of the Anderson Automatic Dredge ; 
each bucketful had to be lifted the full height of the crib at the 
time and deposited in the water or in barges. When the proper 
depth was reached the tubes were filled with concrete, de- 
posited under water. On top of the crib masonry piers were 
constructed, about 40 ft. high ; these piers were 42 X 14 ft. on 
top, and 46 X 18 ft. at the bottom, leaving a margin of about 
1 ft. all around on top of the crib. The piers seem to have been 
constructed of two circular columns of masonry 14 ft. in diam- 
eter, and 28 ft. centres, connected by a rectangular wall 6 ft. 
thick at top, thereby saving some masonry. 



272 A PRACTICAL TREATISE ON FOUNDATIONS. 

7. The difficulties in this method of sinking such large 
structures are many. Great skill is required in handling the 
dredges so as to excavate the material uniformly and close up 
to the sides of the cutting edges at such great depths below 
the surface of the water ; the importance of which, in sinking 
caissons and cribs, is very great, in order to maintain the struct 
ure in a vertical position and prevent careening and conse- 
quent sinking out of line and position. But the success attend- 
ing such efforts fully establishes its practicability, though 
much is left to blind chance. The sinking must, to a great 
extent, take care of itself. Again, if obstacles, such as old 
wrecks, drift, logs, etc., are met with, the removal of these 
causes great trouble and delay with its attending cost, as it is 
by no means an easy job to remove such obstructions in the 
pneumatie caisson, where they can be seen and reached. 
Much of the concrete is of necessity deposited under water, 
the value of which was fully discussed under the head of con- 
crete. If deposited with care, the operation is slow and ex- 
pensive, and without care it is no better than so much broken 
stone, and perhaps not much better with any degree of care. 

Lastly, the factional resistance of the material on the ex- 
terior surface of the caisson is enormous, especially if the sink- 
ing is intermittent, allowing intervals of rest, during which the 
material closes in on the caisson. This requires corresponding 
and enormous weight to overcome it. This resistance may be 
many hundred pounds per square foot of surface. As an illus- 
tration, the writer has made the following calculations on this 
structure: Allowing the low unit of resistance of 250 lbs. per 
square foot, the total resistance must have been 12,000 X 250 
= 3,000,000 lbs. The weight of iron, roughly estimated, 
would be 550,000 lbs., leaving 2,450,000 lbs. of concrete to be 
added, which, at 125 lbs. per cubic foot, would require 20,000 
cubic feet, and allowing a reasonable excess, say 1000 cubic 
yards. Again, the estimated total weight on the foundation 
bed would be 98,806X125 = 12,351,150 lbs. of concrete; 
weight of iron 550,000 lbs.; masonry, 15,300 X 160= 2,448,000 
lbs.; superstructure and load, 2,113,280 lbs, or a total of 17,- 



THE OPEN CRIB. 2J$ 

462,430 lbs., or 13,992 lbs. = 7.0 tons per square foot, not con- 
sidering the frictional resistance, or 5.8 tons, allowing for it. 
The writer regrets his inability to give fuller information on 
this structure. 

8. In 1885 a prominent bridge builder consulted with the 
writer in regard to the cheapest and best method of reaching 
such a depth, as the pneumatic process was considered out 
of the question, and it was feared that the open-crib method 
would prove impracticable on account of the many difficulties 
and objections already mentioned. Being so fully occupied 
at that time, he could not give the necessary consideration to 
the matter. But in the following year he designed a structure 
which was intended to be a combination of the open crib and 
pneumatic caisson, involving some new features which were 
subsequently patented. This will be more fully explained in 
another article, after explaining the pneumatic process. 

9. The third example of the open-crib method will be 
briefly alluded to. It was required to construct a bridge 
across a wide, deep bayou at Morgan City, Louisiana. The 
material of the bed of the stream was very soft, with consider- 
able depth of water over it. Several plans had been discussed 
and submitted while the writer was connected with the road. 
Among them was the Cushing cylinder piers, and timber piles 
with cast-iron cylinders connecting with them at or near the bed 
of the river, as well as others of more or less cost. But the 
work being abandoned, nothing had been done beyond driving 
a few piles. Subsequently, on the renewal of the work, it 
was determined to sink iron cylinders by means of dredging 
out the material. These cylinders were eight feet in diameter. 
Below the bed of the river they were made of cast-iron in sec- 
tions 10 ft. long, with ij-in. metal thickness, strongly bolted 
together through internal flanges. Above the bed of the river 
wrought-iron plate, § in. thick was used, riveted together and 
stiffened with angle irons. The material was dredged out 
from the interior of the cylinder, and as the cylinder settled 
sections were built on top. By these means they were sunk 
a hundred or more feet into the solid material. After reaching 



274 ••' PHAi i£A ! r SE \ FOUNDATIONS, 

the propei depth, they wort- filled with concrete, The stabil- 
ity of such small columns, having long distances unsupported, 
has been repeatedly noticed, They certainly cannot be re- 
garded as possessing any great excess oi stability where they 
arc subjected to heavy pressures or groat shocks, especially as 
the concrete has to be generally deposited under water. The 
above examples illustrate the most recent open-crib and cyl- 
inder constructions in which depths have been reached exceed- 
ing that to which the pneumatic process is generally consid- 
ered applicable, which will now be explained. 



Articj e XLIX. 

rilK PNEUMA riC CAISSON. 

io. BEFORE describing the designs and construction of 
caissons, it will be as well, to avoid repetition, to briefly con- 
sider certain general principles applicable in all cases, and also 
the design and uses of certain parts common to all, 

II. As the name indicates, the air is an essential element 
to be considered, whether simply used to sink the caisson, 1st, 
where a vacuum is made by exhausting the air from the interior 
of an air-tight cylinder or box. ami the unbalanced atmos- 
pheric pressure of Is lbs. per square inch of exposed surface, 
Causing it to sink into the underlying material. This is called 
the vacuum process: it may be said that it is rarely, if ever, 
used now ; 2d, where the air is compressed into a cylinder 
or box, which drives the water out. so that the material can 
be excavated and removed from the interior, which is called 
the air or working chamber, lifting it out in buckets, or 
allowing the air to blow the material out through pipes prop- 
erly regulated by valves, or forcing it out by water pressure. 
This is known as the compressed-air or pneumatic process. 
This latter term is now commonly confined to the use of com- 
pressed air. 

12. The fundamental principle underlying this is simply 



THE PNEUMATIC CAISSON. 275 

that the atmospheric pressure of 15 lbs. per square inch will 
support a column of water, in a tube or pipe from which the 
air has been exhausted, of about 34 ft. high, when the open 
end is immersed in a body of water; or 1 lb. will balance a 

column of 27 ins. high. Practically these heights cannot be 
supported, as a perfect vacuum is almost impossible. Jiut it 
i ! commonly stated that we must have 1 lb. pressure for every 
2\ ft. of depth below the water surface, to keep the water out 
of the working chamber. The actual pressure is 15 lbs. more, 
.as we have to balance a like pressure on the surface of the 
water outside the caisson; this excess is constant for all 
depths. So that if the depth below the water surface is 90 ft. 
the actual air pressure in the caisson is about 45 -f- 15 = 60 lbs. 
The uplifting effect is. however, only 45 lbs. Ord inarily, it 

necessary to reduce the air pressure in the cai 
■■/>:)■■/ materially at times in order to allow the caisson to sink ; 
at other times, however, it is necessary to cease altogether 
adding weight to the caisson to prevent a continuous or too 
rapid sinking. This, of course, depends both upon the actual 
resistance at the lower or cutting edge of the caisson, which 
may or may not be very great, and upon the frictional re- 
sistance on the exterior surface of the caisson and the struct- 
ure upon it. It is therefore, in general, better to have as little 
frictional resistance on the side surfaces as practicable, and to 
provide as great a direct resistance at or a little above the 
cutting edge as is consistent with economy and convenience 
of construction and subsequent ease of prosecuting the work. 

13. As the working chamber should be practically air-tight, 
some special means of entering and leaving the working cham- 
ber must be provided. The air-lock has this object in view, 
and wherever it is placed or whatever its design, it must be an 
air-tight box with two doors, both opened toward the greatest 
ore sure — that is, toward the air-chamber or some air-tight 
channel or shaft communicating with it. These doors open 
inward or downward, and when shut must bear against rub- 
ber gaskets, so as to practically exclude the passage of air; as 
it is the air-pressure itself that keeps the door shut, one of 



276 A PRACTICAL TREATISE ON FOUNDATIONS. 

them will always be open. Strong and tight iron shafts are 
built into the caisson, and should always reach well above the 
surface of the water; the main shaft through which the men 
enter and leave need not be over 4 ft. in diameter. This is 
made in sections, which are bolted together through internal 
flanges, between which rubber bands or some soft and imper- 
vious substance is placed, so as to render the joint air-tight. 
Ordinarily red lead worked up with short strands of ordinary 
lampwick will answer every purpose, it is easily obtained and 
applied. A section of the shaft itself can be converted into an 
air-lock by connecting two doors to it, or a specially designed 
air-lock can be connected with the shaft at its top, bottom, or 
any intermediate point. The writer prefers the air-lock at the 
top, and that it shall also be simply a section of the shaft ; as 
any section can be converted into an air-lock, or the whole 
shaft if so desired. This arrangement possesses many con- 
veniences, and is much safer than when located at or near the 
bottom. It frequently happens that men are driven suddenly 
from the working chamber, and if the lock is at the top they 
can all climb up the shaft and be in safety, while the air is 
being equalized so that the lower door of the air-lock can be 
opened, or if open they can enter the air-lock without delay or 
confusion, or the danger of some one closing the door upon 
them. On the contrary, with the air-lock at or near the bottom, 
the men have no place to enter and be safe if the lower door 
of the lock is closed ; a few minutes' delay may be fatal to many, 
or they all may not be able to enter the air-lock in the con- 
fusion and often cowardice shown by some men in the face of 
danger. The air-lock being a part of the shaft is a mere mat- 
ter of convenience. 

14. A smaller shaft, not over 18 ins. or 2 ft. diameter, for 
letting concrete or other material into the working chamber, is 
also used. It is better to have at least two of these ; they are 
provided with a door at top and bottom only, the entire shaft 
being an air-lock. In addition to these, pipes from 4 to 6 ins. 
diameter are also built into the caisson — the larger diameter for 
connection with the air-hose and force pump for water, the 



THE PNEUMATIC CAISSON. 



277 



smaller diameter for use in blowing out the material. There 
should be a number of these distributed around the caissons. 
All pipes should be provided with the best valves, and when 
not in use should be capped with a cap screwed on to the pipe 
above the surface and stopped by plugs below to prevent any 
possible chance of a sudden escape of the compressed air. 

15. The use of the air-lock can now be easily understood. 
Compressed air is rarely, if ever, required until the caisson 
rests firmly on the bed of the river in its proper position for 
the pier. As soon as it does so rest, the doors being both open, 
air connections are made between the proper pipe and the air 
compressors ; all other pipes or avenues through which the air 
could escape being closed, the lower door is lifted by a small 
tackle against its bearing, and the compressors are then started. 
It requires only a few pounds of pressure to hold the door in posi- 
tion. When the pressure gauge indicates a pressure required for 
the then depth, men enter the air-lock through the other door- 
way, its door swinging freely. This door is then lifted into posi- 
tion by the lock tender on the outside ; the valve in the upper 
door or in any other position in which it may be placed is 
closed, and the valve in the lower door or opening into the 
main shaft at some point below the air-lock is opened. The 
compressed air rushes into the air-lock, and continues to do so 
at a lessening velocity until the air in the lock is at the same 
pressure as that in the working chamber; it is then said to be 
equalized. The lower door would now open of its own weight, if 
it were not held in position by a tackle in the air-lock. As the 
pressure on both sides is now the same, the lock tender on the 
inside allows the door to open, and the men descend by 
means of an iron ladder fastened to the sides of the shaft into 
the working chamber. A thorough examination is made to see 
that there are no leaks ; complete the interior bracing if not 
already completed, and see in short that everything in the in- 
terior is all right. To get out they ascend the shaft, enter the 
lock through the lower or open door-way, lift this door to its 
place, close the lower valve, and open the upper valve, which al- 
lows the compressed air in the lock to escape into the open air. 



278 A PRACTICAL TREATISE ON FOUNDATIONS. 

In a short time this pressure will be reduced to that of the at- 
mosphere, the upper door is lowered by the outside lock ten- 
der, and the men pass out. The above operations have to be 
repeated each time that a man passes in or out of the caisson. 

16. If everything is ready below, a gang or shift of men 
now passes into the lock and thence into the caisson, and the 
work of excavating the material in the caisson is commenced. 
So long as the depth is not over from 60 to 70 ft. below the 
water surface, only three gangs or shifts are required during 
the 24 hours ; each shift working 8 hours and resting 16 hours,, 
coming out to lunch at about the middle period of their work- 
ing time. This will consume from ^ to f hours, so that they 
only remain about 3! hours in the caisson at a time. For 
greater depths the men are divided into 4 shifts, working 6 
hours each, with the same interval of rest during this time, or 
actually remaining in the caisson about 2\ hours at a time. A 
full shift consists of 1 foreman and 10 to 20 men, according to 
the size of the caisson, and one outside and one inside lock 
tender; this not including the machinery men, such as engineers, 
firemen, pipe-fitters, etc., and one or two handy men, and over 
all a general superintendent. The general duties of these men 
and the mode of procedure will be explained later. 

17. One thing can be relied on : so long as the air pressure 
required by the depth is maintained, the water will not rise 
above the extreme lowest line of the cutting edge of the cais- 
son, and in sinking through some materials water has to be 
pumped into the caisson in order to carry on the work. The 
caisson must be heavily weighted before the air pressure is put 
on, or a dangerous tendency to lift and careen will exist. The 
end of the air pipe in the caisson should be fitted with an 
automatic valve, opening into the caisson, so that should the 
compressors stop from any cause, the air pressure will close the 
valve and prevent the escape of the air ; a simple circular plate 
of iron with a rubber gasket sliding freely on two small iron 
rods attached to the end of the pipe, and allowing a play of \\ 
to 2 ins., answers well the purpose, as it does not prevent an 
easy flow of air into the caisson, but closes instantly on the air 



THE PNEUMATIC CAISSON. 2 J 9 

compressors stopping. A small plunger pump connected with 
the compressors forces a certain amount of water in with the 
air to prevent its getting too dry and hot; this is all important. 
At a depth of 80 or 90 ft. the usual temperature in the work- 
ing chamber will be from 85 to 90 Fahr. This is due to com- 
pressing the air. The temperature of the air in the air-lock 
will rise to 106 to 125 Fahr., the temperature in the air cham- 
ber being reduced by the moisture and the cooler surfaces on 
the interior. 

18. As to the effect on men working in compressed air, a 
few remarks may be interesting and instructive. 

While in the air-lock everybody is more or less affected 
with pains in the ears, known as " blocking." With some it is 
intense, and many have to reverse the valves and get out before 
the pressure is equalized, but the act of swallowing, blowing 
the nose, or closing the nose and mouth and exhaling the air 
from the lungs will give ready relief. This trouble may arise 
either on entering or leaving the lock. Again, in about 15 or 
20 minutes after coming out of the caisson many men are at- 
tacked with severe pains in the limbs ; these may be more or 
less intense and may last a day, a week, and sometimes longer, 
but seem to leave no permanent effects. These pains are known 
as the " bends." Returning into the compressed air gives instant 
relief, but they will probably return on again leaving ; this 
trouble is common, but very many escape entirely. 

A more serious trouble sometimes happens, resulting in a 
paralysis of some part of the body. This will in general be of 
a temporary nature, but is sometimes lingering and often 
permanent ; but a small per cent of men will be thus attacked. 
And lastly, some severe cases of paralysis occur, from which 
the men die within a few hours or in a day or two. Occa- 
sionally a blood vessel in the nose or ear will be broken, 
some men losing their hearing from this cause ; on the con- 
trary, for some forms of deafness it has been claimed that 
exposure to compressed air affords more or less relief. Many 
opinions and theories have been advanced as to the prin- 
cipal causes of these troubles ; but most, if not all, are unsatis- 



2 SO A PRACTICAL TREATISE ON FOUNDATIONS. 

factory, if not entirely erroneous. The writer had about five 
years of almost continuous experience in works of this kind, 
going almost daily into the caissons and remaining often in 
the pressure for hours at a time ; and though not conscious of 
any harmful effects of either a temporary or permanent charac- 
ter so far as he was concerned, he made a careful study of the 
effects on others, and believes that much of the trouble is due 
to carelessness and indifference on the part both of the men 
and managers, and even under these circumstances he believes 
that perfectly healthy men have but little cause of uneasiness. 
19. In going through the air-lock, as has been stated, the 
temperature rises in a few minutes from that of the atmosphere 
at the time, whether during freezing or milder weather, to at 
least 106 Fahr., causing a profuse perspiration to set up in a 
few minutes. This continues while below. On passing out 
through the air-lock, as the pressure rapidly falls, so does the 
temperature ; the perspiration is suddenly checked, and a cold, 
clammy sensation follows. The men, with little or no clothing 
on, pass out into a temperature very much lower, often well 
below the freezing point ; they sit in exposed positions around 
the engine room or elsewhere for a half hour or more, and 
again go through the same ordeal. Entirely inadequate ar- 
rangements for their protection or comfort are sometimes pro- 
vided. Entering and leaving the caisson often happens many 
times in a period of six or eight hours. While working below, 
even if the working chamber is lighted by electricity, which is 
not always or even generally the case, it is necessary to use can- 
dles to a great extent ; these are especially prepared, and would 
burn but slowly under ordinary conditions, yet burn freely in 
the compressed air, saturating the air with large quantities of 
soot, which the men breathe freely and constantly, getting 
their system and lungs filled with it, and expectorating contin- 
ually a black mass from their lungs — this continuing for weeks 
even after completing the work. The above conditions are 
doubtless the most potent factors in causing the caisson dis- 
eases. It is commonly believed that the actual pressure is the 
cause. There is absolutely no evidence to sustain this opinion, 



THE PNEUMATIC CAISSON. 28 1 

beyond the blocking of the ears, which is evidently caused by 
an almost infinitely small period in time of an unbalanced 
pressure on the outside or inside of the drum of the ear, as 
in all other respects the condition of the physical man is per- 
fectly normal, no matter how long he may remain under the 
.pressure. There is no observable compression or subsequent 
puffing of the flesh, no restraint or other change in his move- 
ments, or in the use of himself, except that he will work and 
hit harder and feel more or less exhilaration, which is no doubt 
due to an increase in the supply of oxygen, which even over- 
comes the lassitude that would otherwise be caused by such a 
profuse and continued perspiration. 

20. If the writer is right in his views, the remedy or cer- 
tainly an amelioration of the troubles is simple and not ex- 
pensive. 

i. Select only healthy men for this work. Little or no 
attention is given to this. The only rule is to get men and 
get them as cheaply as possible. From 20 to 25 cents an hour 
for eight hours' work is the usual price paid. Men will do 
from one and a half to two times the work in the caisson that 
they will do outside. 

2. Prevent, at least, to some extent, the sudden alterations 
•of temperature through 70 to 90 Fahr. day or night, and in 
all kinds of weather. A common reply to this is that the men 
who regulate the valves are instructed to pass the men through 
slowly, and that the valves are worked entirely by the men in 
the locks, who will be the sufferers; but yet valves of compar- 
atively large apertures are given them. If they were smaller, or 
if not fully opened, the time would be much longer in passing 
in and out, during which time all work must be suspended in 
part or entirely ; this means loss of time and money, which is 
not necessary. Provide then a lock or chamber connected 
with the main lock, in which men can enter without obstruct- 
ing the main lock, which can be maintained at a bearable tem- 
perature, while the air is being equalized ; let the men wash 
and dress themselves, and come out in some sort of comfort. 
Any man will get out of a temperature of 106 to 125 as fast as 



282 A PRACTICAL TREATISE ON FOUNDATIONS. 

possible ; nor will he remain in a cold, clammy condition, 
longer than possible. Although it may not be practicable to 
do away entirely with candles, the use of them can be materi- 
ally lessened. These remedies will be attended with some ex- 
pense, but they will greatly add to the health and useful- 
ness of the men, and doubtless enable us to reach much, 
greater depths than ioo ft. by the pneumatic process with 
vastly less danger and suffering than now exists at depths 
under ioo ft. below the water surface. 

21. A code of signals is always used, by which the men in 
the caisson can communicate their wants to those above. The 
method of simply knocking with an iron bolt on the iron shaft 
or pipes is as satisfactory as any that could be devised ; it gives 
a clear, ringing, unmistakable sound, i knock for more air, 
2 for less, 3 for starting the water-pump, 4 that the men are. 
coming out, etc., varied as may be desired, answers all prac- 
ticable purposes. The outside lock tender above all should 
be a faithful, wakeful, and reliable man, ever on the alert 
for signals from below, as all wants should be supplied immedi- 
ately. 

22. The immediate effect of reducing the air pressure even 
by only a few pounds is to set up a dense fog. All oscilla- 
tions in the pressure should therefore be avoided as far as 
practicable, and this together with the greater tax upon the 
capacity of the compressors is the main objection to forcing 
out the material through the pipes by means of the compressed 
air ; a method which in other respects is more rapid, and in 
many cases more economical and satisfactory, than any other 
of removing the material from the working chamber. A 4-in. 
pipe will easily carry gravel, sand, mud, and bowlders up to 
3f ins. diameter. It requires careful regulation or feeding, 
however, to avoid choking the pipes, and requires a considera- 
ble quantity of surplus air. For these reasons a sand or mud 
pump is often or commonly used. 

23. A few remarks on the necessary machinery will be useful. 
Several boilers of large steam-producing capacity are essen- 
tial ; much time and money are lost and great inconvenience 



CONSTRUCTION OF PNEUMATIC CAISSONS. 283 

caused by the want of them. The compressors have to be run 
continuously day and night, and often in addition large force 
pumps, electrical machinery, and pumps for keeping water out 
of the cribs while concreting and out of the coffer-dams while 
building the masonry. And after making a liberal allowance 
for these purposes, at least one extra boiler should be provided, 
as some wear out, some need repairs, and a largely increased 
supply of steam is sometimes required. One good-sized double 
compressor will generally supply the requisite amount of air; 
another should always be in reserve. At least one large 
double force pump should be provided. Other engines, 
pumps, etc., of smaller power will be required. A large 
supply of pipes, hose, machinist tools, etc., should be provided, 
and with them a first-class machinist, as a large amount of 
fitting, repairing, etc., must be done on the work and promptly, 
whether required by day or by night. This machinery is 
generally mounted on one or more barges and tied to the 
structure. All connections between the machinery and the 
pipes, etc., should be made by the best make of hose, to avoid 
any possibility of breaking, bending, or otherwise deranging 
any of the pipes. As a sudden escape of air may cause not 
only loss of life, but serious damage to the structure. No worn- 
out, broken-down machinery or fittings of any kind should be 
allowed. 

Article XLIX. 
CONSTRUCTION OF PNEUMATIC CAISSONS. 

24. THE general design of caissons is the same whether 
made of wood or iron, and consists of three parts, as follows : 
1st, the walls of the working chamber ; 2d, the deck or roof of 
the caisson, with its necessary shafts, pipes, etc., built into and 
through it ; and 3d, the necessary trusses, braces, etc., to 
strengthen and stiffen the walls and the roof. 

A short description of the design and construction of some 
of the typical timber and iron caissons heretofore used wilL 
now be given. 



284 A PRACTICAL TREATISE ON FOUNDATIONS. 

25. The caissons for-the foundations of the New York and 
Brooklyn suspension bridge are about the largest timber cais- 
sons constructed in this country. They were rectangular in 
cross-section. The bottom dimensions 172 X 102 ft., and at 
top 165 X 95 ft., 3 1^ ft. high; thickness of the roof 22 ft., and 
were sunk 78 ft. below mean high-tide. The frictional re- 
sistance on the sides varied from 280 to 600 lbs. per square foot. 
Estimated pressure on a foundation-bed of sand, 7^ tons per 
square foot. The design of the caisson was simple. All of 
the timbers composing it were 12X12 ins. in cross-section and 
laid horizontally and well bolted together. The height of the 
working chamber was 9J ft. ; the thickness of the walls varied 
from 6 ins. at the cutting edge to 9 ft. where it was joined to 
the roof. This was built solid of timbers laid in courses one 
on top of the other, crossing each other and bolted together. 
The inner slope of these walls were 1 to 1, the vertical sec- 
tion being V-shaped. These were connected by cross-wall, 
also built solid, dividing the working chamber into compart- 
ments communicating by openings in the cross-walls. On 
these walls a solid roof of square timbers in courses crossing 
each other, 22 ft. thick, was constructed, thoroughly bolted 
together. A cast-iron shoe was placed on the cutting edge, 
and under this plate-iron was bent extending up both the 
outer and inner slopes of the wall, and in one of the caissons 
the entire inner surfaces of the chamber was lined with plate- 
iron, and also between the fourth and fifth courses of the roof 
a layer of tin was placed and bent downward on the outside, 
reaching to the iron plate above mentioned. These metal 
linings were used to prevent damage from fire, and also to 
insure air-tightness. The deck timbers were not placed in 
close contact, the intervals being filled with concrete or mor- 
tar. The usual pipes, shafts, etc., were built through the roof, 
and in addition a large shaft 8 ft. in diameter, open at both 
ends, the lower end reaching into an excavation at the 
bottom filled with water, the water extending up the shaft. 
This was used for removing large bowlders, etc., by means of 
specially designed hooks or buckets worked from above. This 
was about the only novel or unusual feature in the design. 



CONSTRUCTION OF PNEUMATIC CAISSONS. 285; 

One of the caissons caught fire, which, being supported by a 
large quantity of oxygen, burnt its way to a considerable dis- 
tance into the roof. The caisson had to be flooded to extin- 
guish the fire. It is not an unusual habit of caisson men to 
use the flame of a candle to detect leaks in the caisson. There 
is always some danger in the presence of so much oxygen and 
combustible material of starting a fire. Other methods of 
determining air-leaks should be used. 

26. The caissons for the St. Louis bridge, though com- 
monly called iron caissons, were largely constructed of timber 
and iron combined. The walls of the working chamber were 
composed of iron plates, stiffened by angles and brackets ;. 
timber also being fastened to the walls, giving stiffness and 
also affording an increased bearing surface. The decks of 
these caissons were formed by deep and strong girders or 
beams, resting on the outside, and cross-walls of the air cham- 
ber, to the under side of which plate-iron was riveted or 
bolted, forming a strong and air-tight roof. The space be- 
tween the girders was filled with concrete or masonry, and 
the regular masonry for the piers was then built on top of 
this. As the sinking progressed, a timber coffer-dam, sheathed 
on the outside with plate-iron, was built up, in which the ma- 
sonry was constructed. In the Brooklyn bridge no coffer-dam 
was used ; the masonry commenced on the deck of the cais- 
son, and was built up as the caisson settled, so as to keep its 
upper surface above the water-line. In the St. Louis bridge 
large open shafts were built in the masonry; this was lined 
with brick and timber, so as to make it water-tight. The air- 
lock was placed at the bottom of the shaft. The writer has 
heard it stated that in this, as in some other cases, the en- 
gineers placed the air-locks at the bottom, leaving long open 
shafts, reaching above the surface of the water, so that the 
men might ascend the ladders or the shafts in the ordinary 
air. Whether this is true or not, he does not think that cais- 
son men would hesitate to prefer to make the ascent in com- 
pressed air, as there is always a feeling of lassitude and an indis- 
position to exerting one's self immediately after coming out of 
compressed air, to say nothing of the feeling of safety when the 



"286 A PRACTICAL TREATISE ON FOUNDATIONS. 

air-lock is at the top of the shaft. The horizontal cross-sections of 
the St. Louis caissons were hexagonal in shape to conform approx- 
imately to the shape of the masonry piers ; their dimensions at 
the bottom were 83 X 70 ft., and 64 X 48 ft- at a point 14 ft. 
above. A section of this kind is easily built in iron, but for tim- 
ber caissons it would present some objectionable features. These 
caissons, after sinking through water and sand, finally rested on 
rock at a depth of ioo,f ft. below the water surface. The sand 
was removed during the sinking by the sand pump, the princi- 
ple of which is the same as the ordinary injector, and will be 
explained under another example of caissons. The working 
chamber of one of the caissons was filled entirely with con- 
crete. But, as a matter of economy in the other, a wall of 
concrete was built entirely around the working chamber, and 
the interior space was filled with sand. The estimated press- 
ure on the foundation-bed was 19 tons per square foot. At 
the time of constructing this bridge the caissons were the larg- 
est ever used, and the depth below the water surface the great- 
est ever reached. All things considered, this bridge is one of 
the greatest structures in the country. 

27. The latest, and perhaps the largest, structure of the 
kind has recently been completed across the Mississippi River 
at Memphis, Tennessee. This bridge was opened for traffic 
May 12, 1892. 

Although no full and official publication has been made in 
regard to this structure, the following data and description 
have been obtained from reliable sources. 

The total length of the structure is 7997 ft., divided as 
follows : 

Iron viaduct approach to bridge proper 2300.00 ft. 

Timber trestle " " " " 3100.00" 

Bridge proper, divided into 5 spans by 6 piers. The length of the 

spans were as follows : 1 span 225.83 = 225.83 " 

1 cantivever span. Cantilever arms each 169.38 ft.; suspended 

truss, 451.66 ft. Total length 790.42 " 

1 span cantilever arm 169.38 It., and truss 451.66 = 621.04 " 

1 through truss 621.06 " 

J deck " 338.75 " 

Total length 7997. 10 ft. 



CONSTRUCTION OF PNEUMATIC CAISSONS. 287 

Tlie masonry piers varied in height from 93 to 158 ft., con- 
structed of Georgia granite-face stones and Indiana limestone 
backing. 

There were five pneumatic caissons, varying in horizontal 
dimensions from 40 X 22 ft. to 92 X 47 ft., and in height from 
40 to 80 ft. from the bottom of caisson to bottom of masonry,* 
and sunk to depths from 78 to 151 ft. below high-water As it 
was apprehended that a scouring action might be caused by the 
obstruction to the current when the caisson was lowered to the 
bed of the river, rendering it difficult to properly level and 
locate the caisson in the commencement of the work, large 
willow mattresses, laced with wire, were constructed and sunk 
to the bed of the river over the site of the caisson by sufficient 
weight of rock. These mattresses were 240 x 400 ft. square, 
this affording a large, protected surface on the bed of the river. 
Upon these the caissons were lowered ; and when they rested 
firmly and the air-pressure put on, men descended into the 
working chamber and cut through the mattress along the cut- 
ting-edge of the caisson, allowing the caisson to sink through 
the mattress. Total distance from top of masonry to founda- 
tion-bed, which was composed of clay, was about 199 ft., and 
below high-water about 131 ft., and 96 ft. below low-water. 
The greatest immersion was 108 ft. 

The anchor pier on land was founded about 50 ft. below 
the surface, and weighed 2500 tons. Long iron rods passed 
through the masonry, and were fastened to a network of iron I- 
beams under the masonry. This made the entire mass of the 
pier act as a unit in balancing the moving load on the canti- 
lever. The cost of this structure was about $3,000,000, 
and required about three years in its construction. The under 
side of the trusses were 109 ft. above low-water and 75 ft. 
above high-water. Height of trusses, about 78 ft., and width 
between trusses, 30 ft. between pin centres. The notable 
features of this structure were the great length of spans used, 

* The designers of these structures seem to make no distinction between 
the caisson proper and the crib above it; calling the entire structure a caisson. 
The writer calls that part a caisson shown in Fig. 3, Plate XVIII. A crib 
above may or may not be used. 



288 A PRACTICAL TREATISE ON FOUNDATIONS. 

especially in the cantilevers, and the use of large mattresses to 
prevent scouring- action in the early stages of the work. Total 
weight of superstructure, 19,541,700 lbs., or 9771 tons. 

The above are examples of the largest structures now in ex- 
istence in which pneumatic caissons of wood alone or wood and 
iron combined were used in the construction of the foundations. 
28. A description of an all-iron caisson will be given, ac- 
companied with a skeleton sketch of the caisson itself — inter- 
esting and instructive not only as a typical iron caisson, but 
also from the special difficulties in the way of its completion, 
as well as in its entire lailure. It was a Government work, and 
the object was to construct a lighthouse off the coast of North 
Carolina, on what is known as Diamond Shoals. The Govern- 
ment engineers advertised for plans and estimates of cost, 
leaving the matter of design and methods to be pursued to 
those desiring to bid on the work. The result was that three 
proposals were offered by American builders, differing some- 
what in plans, cost, and methods of procedure. Owing to the 
exposed location of the structure and the severe and sudden 
storms, with the consequent excessive scouring of the shifting 
sands, the greatest difficulty necessarily arose in the commence- 
ment ; and the success of the enterprise depended mainly on 
choosing the most favorable time and securing a good hold be- 
low the surface between the periods of the prevailing storms. 

One of the plans called for a large timber caisson sur- 
mounted by a strong double-walled iron crib constructed on 
top of it ; the spaces between the walls of the crib to be 
filled with concrete, in order to furnish necessary weight to 
sink the caisson. 

Another plan in which both caisson and crib were to be 
constructed principally of timber and concrete used in the crib 
to sink the caisson. In both cases the working chambers of 
the caisson were to be filled ultimately with concrete. 

The third plan, which was accepted by the engineers, pro- 
vided for executing the work by the open-crib process, with 
alternate proposition for pneumatic caisson, if found necessary. 
This can better be described in the words of the contracting 
parties, Messrs. Anderson & Barr. 



construction of pneumatic caissons. 289 



Diamond Shoals Lighthouse. 

Extracts from the specification of Anderson & Barr, con- 
tractors, are as follows : 

" We propose to sink the foundation 100 ft. below the bed 
of the shoal, if the material in the way of sinking the founda- 
tion is such that we can remove it by dredging. If the 
material is such that we must resort to the use of compressed 
air in order to remove it, we will sink the caisson 80 ft. below 
the low-water line, unless rock is encountered before that 
depth is reached. The foundation to consist of an iron caisson 
filled solidly with cement concrete. Concrete is to be made of 

1 part of Portland cement, 2 parts of sand, and 4 parts of 
stone broken so as to pass through a 2-in. ring. The founda- 
tion caisson is to be built of cast-iron plates, with a bottom 
section of wrought steel. The total height is 155.5 ft- The 
wrought-steel bottom section is of cylindrical shape, 54 ft. 
diameter and 30 ft. high. On top of this is bolted a cast-iron 
conical section 20 ft. high, of 54 ft. lower and 45 ft. upper di- 
ameter. On top of this is placed the main body, which is of 
cylindrical form and of 45 ft. diameter, and which continues of 
even shape to the level of the base of the lighthouse tower. 
Through the whole body of the caisson parallel with its axis 
pass four water-tight steel cylinders of 9 ft. diameter, through 
which the ground is excavated from under the caisson. 

"At 19 ft. high from the bottom edge of the caisson these 
cylinders widen out into irregular conical shapes, which end at 

2 ft. 9 ins. above the bottom of the caisson in the circumferen- 
tial cylinder shape and in a cross-bulkhead of 3 ft. height, 
which divides the area on the bottom of the caisson into four 
equal sectors of the circle. 

Thus for 2 ft. 9 ins. height the bottom of the caisson con- 
sists of a single thickness of cylindrical outside plates, and 
bulkheads consisting of a single thickness of plate which divide 
the area of the circle into four equal parts, each of which is 
provided centrally over it with an open vertical tube 9 ft. 



290 A PRACTICAL TREATISE ON FOUNDATIONS. 

diameter, for the purpose of dredging its quarter compartment. 
The bottom circle of cylinder plates of 6 ft. height is of f-in. 
thickness. The cross-bulkhead plates are of f-in. thickness. 
These central straight plates, as well as the outside circle 
plates, are provided with stiffening brackets of f-in. thickness 
and 4-in. angle-irons. All the other plates of the wrought 
bottom section is of t^-in. thickness, both the outside cylinder 
and the interior cones and tube ends. Four-inch angle-irons, 
running vertically the whole length of the section and 4 ft. 
apart, are riveted to the interior of the cylinder, and corre- 
sponding ones to the conical bottoms, and the dredging tubes 
are braced together by 4-in. angle-iron bracing in such form as 
to generally stiffen the structure against both outside and in- 
side strains. Similar angle-irons brace those portions of cones 
and dredging tubes together which face one another. The 
top of the wrought section is provided with a 6-in. angle-iron 
on the inside of the cylinder, to which the cast-iron cone is 
bolted. This cone, as well as the cylindrical portion of 45 ft. 
diameter above the cone, consists of cast-iron plates of i^-in. 
thickness, and of such horizontal length as to make the cir- 
cumference of 20 plates and of 5 ft. height. The plates are 
provided with planed flanges forming 6-in. depth of joint all 
around them, strongly bolted together with i-in. bolts and 
nuts, and laid so that the vertical seams of different layers 
break joints. Lugs are cast on the plates, from which 4-in. 
angle-iron braces run to the nearest of the four central tubes. 
These latter are of a uniform diameter of 9 ft., made of ^-in. 
plate in sections 5 ft. high, like the outside plates, and provided 
on top and bottom with 4-in. angle-iron outside rims for join- 
ing them by means of i-in. bolts and nuts. The braces from 
the cast-iron circumference plates are attached to these rims; 
also the braces by which the tubes are braced to one another. 
For convenience of transportation and erection the cylinders 
are in halves, joined by 4-in. angle-irons and i-in. bolts on the 
vertical seams. These tubes extend up to 2 ft. above the 
high-water line, and above that point the circumference plates 
are braced by turnbuckle bolts of i^-in. diameter. 



CONS 7 R UC TION OF FA F: UMA 7 IC CA IS SO A r S. 29 I 

The whole interior of the caisson, including the tubes, will 
be filled with cement concrete, except that seven cylindrical 
vaults will be built in the floor of the towers. On the top sur- 
face of the concrete a cast-iron base of 42^ ft. outside diameter 
and 2 ft. width, if-in. thickness will be placed, on which the 
tower will be erected. 

Total weight of the structure, 3,832,400 lbs. 

Concrete about 10,000 cubic yards, and contract prices for 
the structure completed in place, $485,000. 

The above is copied from the columns of the Engineering 
News. 

For elevation, vertical section, and plan, see Figs. 1 and 2, 
Plate X. 

29. The Cairo bridge across the Ohio River, near its 
mouth, was constructed in 1887-88 by the Union Bridge Co. 

The superstructure of the bridge proper consists of 12 
single-track steel spans, varying in length from 249 ft. to $i8|- 
ft. The piers supporting the longer spans rested on pneu- 
matic caissons sunk 75 ft. below low-water. The masonry 
started 25 ft. below low-water and 10 ft. below the bed of the 
river. Length between end piers, 4644I ft. The approach on 
the Kentucky side consisted of 21 spans of 150 ft. = 3150 ft. 
and 4594 ft. of timber trestle. On the Illinois side the ap- 
proach consisted of 17 spans 150 ft. and 1 span 106J ft. = 2550 
ft. and 5327 ft. of timber trestle. All approach spans rested 
on piers composed of two steel cylinders filled with concrete 
and resting on piles. 

The river bed is alluvial soil ; some loose rock was found at a 
depth of 175 ft. It was determined to use the caissons for the 
foundations, as the apprehension of encountering logs, wrecks, 
etc., rendered the use of the open crib sunk by dredging risky 
and uncertain, and the loose nature of the material together 
with the rapid currents in floods precluded the use of piles. 
The dimensions of the caissons were 30 X 70 ft. and 26 X 60 ft. 
The height of the caissons and cribs were about 50 ft. The 
caisson proper was 16 ft., the pitch of the working chamber 8 
ft., with two courses of solid timber forming the deck proper; 



29 2 A PRACTICAL TREATISE ON FOUNDATIONS. 

and on top of this six courses of timber of open-work crossing 
each other, and on this 34 ft. of open-work crib, similar to 
the upper 6 courses of what is called the caisson, leaving there- 
fore 12-inch spaces between all of the timbers in every 
direction, except that the cross-braces divided the entire crib- 
work into a scries of hollow prisms 7 ft. sq., extending from 
the top to the solid courses of the deck. The outside walls 
were covered with two courses of 3-in. oak plank, the inner 
layer placed diagonally and the outer layer vertically. The 
walls of the working chamber were V-shaped and built hollow. 
The whole was tied together by screw and drift bolts and 
spikes. The working chamber was lined with 3-in. plank, 
caulked and painted with two coats of white lead to prevent 
air leakage and aid in lighting the interior. The shoe of the 
caisson was made of iron plates f-in. thick and 36 ins. deep. 
The main shaft was only 3 ft. in diameter; supply shaft 2 ft. 
The air-lock was made of ^-in. iron plates 9 ft. long, 6 ft. wide, 
and 7 ft. high, with circular ends 3 ft. radius, and was divided 
into compartments forming independent locks, and was placed 
8 ft. above the deck of the caisson." The usual air, water and 
discharge pipes were used. The sand in the working chamber 
was removed by the Monson sand pump, somewhat different 
in design from the mud pump to be described presently, but sim- 
ilar in principle. The blowing-out process was also used, and to 
avoid a too great waste of air when the material was blown out 
dry, the pipe was extended below the cutting-edge so as to be 
underwater. The maximum sinking in 24 hours was 10.63 ft., 
but the usual progress in clean sand was from 2 to 4 ft. daily ; 
in some caissons it was only 1.1 to 2 ft. The greatest immer- 
sion was 94.2 ft. The calculated frictional resistance was from 
597 to 715 lbs. per square foot of surface (the estimated 
resistance before sinking was 400 lbs. per square foot) at a 
depth in the sand of 86.42 ft. After several cases of paralysis 
and two deaths, a warm, comfortable room was fitted up, 
and also hot baths and coffee were provided, after which 
no further serious illness occurred. The temperature of the air 
in caisson was also cooled by passing through coils of pipe kept 



CONSTRUCTION OF PNEUMATIC CAISSONS. 293 

surrounded with cool water, lowering the temperature from 
125 to 90°. The time of working the men varied from 8 
hours to i£ hours per shift, allowing from 16 to 21 hours of 
rest during the 24 hours. Portland cement concrete was made, 
1 cement, 2 sand, 3 broken stone. Louisville cement concrete, 
1 cement, 2 sand, 3$ broken stone. The piers for the ap- 
proach spans consisted of two cylinders 8 ft. diameter, placed 
18 ft. centres, braced together. Metal thickness £-in. plates, 
spliced on the inside. A pit was excavated 8 ft. deep, in 
the bottom of which twelve oak piles were driven ; the pits 
were then partly filled with concrete, and the cylinders placed 
on the concrete. Concrete was then packed around the cylinders 
below the surface and also in the cylinders to the top, and was 
left about \ in. above. Over the top a steel plate \ in. thick was 
placed. After allowing 400 lbs. per square foot of surface on 
the caissons for frictional resistance, and after deducting the 
buoyant effect of the water and sand (respectively 22,756 cu. 
ft. and 78,000 cu. ft.) amounting to 9544^ tons, from the total 
weight of 15,865.9 tons, the estimated weight on the founda- 
tion-bed was 6291.4 tons, or 3 tons = 6000 lbs. per square foot. 
The precautions taken for the safety and comfort of the men 
certainly are to be highly commended. The writer hesitates to 
criticise the constructions of men of so much experience, knowl- 
edge, and skill ; but he thinks that cutting up the space in the 
cribs with timbers in such numbers separated by only 12 ins. of 
space is a faulty construction, and must necessarily require either 
a great deal of labor and care to fill around and under so many 
square timbers, — round logs for cross-braces would to some ex- 
tent remedy the objection, — or if the work is carelessly done 
there must exist many hollows and open spaces. The position 
of the air-lock near the bottom can hardly be recommended.* 

* Only the caisson proper is shown in Plate XVIII. The roof consists of two 
solid courses of timbers, and six courses of timbers built open, as shown in Fig. 3. 
The crib can be built on top of the caisson to any desired height, 34 ft. in this 
case, and is built open, as shown in Fig. 3. The V-shaped walls can be built 
hollow and filled with concrete, or they can be solid built with timber, as shown 
on the right in Fig. 3. 



294 A PRACTICAL TREATISE ON FOUNDATIONS. 

These parties, however, have put in more caissons than almost 
any others. The success which has attended their works cer- 
tainly cannot be criticised, and it must be presumed that they 
consider it economical and satisfactory in every respect. See 
Figs, i, 2, 3, 4 and 5, Plate XVIII. 

29^. Having described briefly the caissons of the above 
large bridges, we will now consider in somewhat greater detail 
the design and construction of the caissons used by the writer 
on several large bridges, as the Susquehanna Bridge, Havre 
de Grace, Md., the Schuylkill Bridge, Philadelphia, Pa., and 
the Tombigbee River Bridge, Ala. The caissons were nearly 
as large, and the depths sunk were about as great ; hence the 
details of construction, methods of sinking, etc., would be 
equally applicable to any of those already described with few 
modifications of minor importance, while in connection with 
these the descriptions will be based upon actual experience, as 
the caissons were designed by, and the work executed under the 
direct supervision, of the writer; but as applied to the others they 
would be purely a compilation from the descriptions of others. 

The design and construction of the caissons were the same 
for the three bridges. There were 5 caissons in the Susquehanna 
River Bridge, varying in dimensions from 63.27 X 25.93 ft. to 
78.19 X 42.27 ft. and a general thickness of roof of 8 ft. The 
widest caisson had a roof 10 ft. thick ; these were built solid, of 
courses of 12 x 12 in. pine timber. At the Schuylkill there 
were two rectangular caissons 65.5 X 23.5 ft., one octagonal 
caisson 50 ft. in diameter of circumscribing circle for pivot 
pier, and one nearly square caisson 44 X 45 ft. for a U-abut- 
ment ; the roof of this latter was 10 ft. thick, of the others 
8 ft. thick — the depths sunk varying from 40 to 90 ft. below- 
low-water. 

At the Tombigbee Bridge there were two rectangular 
caissons 45 X 23 ft. and one octagonal caisson 24 ft. diameter 
for the draw pier. These caissons were sunk only about 33 ft. 
below low-water, but the excavation was continued about 9 ft. 
below the cutting-edge of the caisson to a point about 42 ft. 
below low-water and 82 below high-water. 



CONSTRUCTION OF PNEUMATIC CAISSONS. 295 

30. On all of these caissons cribs were constructed and filled 
with concrete, varying in height from 20 to 40 ft. of the same 
horizontal sections as the caissons at the top, which was about 
20 ins. less in each dimension than that given above, as the 
caissons were 15 ft. high, and had a batter all around of f- in. 
to each vertical foot. 

31. Coffer-dams were constructed on top of the cribs from 
20 to 40 ft. high, according to the depth of the water in which 
the masonry of the piers was constructed. 

32. A description of one caisson, crib, and coffer-dam will 
answer for all, with a few modifications for the octagonal forms 
required by its shape. The descriptions will be better and 
more easily understood by reference to Plates XIII, XIV, XV, 
XVI, and XVII. The plates show horizontal and vertical 
sections, plans, details, etc., of caissons, cribs, and coffer-dams. 
The caisson was constructed by first building a solid wall 
of five or six courses of timber, \2\ X 12 ins. cross-section, 
surrounding the required space, and built with the proper 
batter. On the outside of this, timbers, 12 X 14 ins. X 14 ft., 
were placed all around, extending 2 ft. below the timber- 
wall and 6 ft. above ; the lower edges of these pieces were cut 
to a bevel, the lower cutting-edge being 3 inches thick. On 
the inside of the wall three courses of 3-in. plank were placed, 
crossing each other diagonally, and on the inside of this a 
single course placed vertically. For convenience of calking, 
the courses of plank were cut to a level with the top of the 
wall and reached to within one foot of its lower edee. The 
whole was then bolted together by both screw and drift- 
bolts, as shown in the drawings. Each layer of plank was 
also spiked with two spikes, 5^ inches long, to each lineal 
foot of plank. Then plank was also spiked in one layer on all 
interior surfaces below the courses of plank above mentioned. 
This completed the walls of the working chamber. The deck 
courses were then placed between the verticals projecting up- 
ward and resting on top of the timber-wall and the four 
courses of plank on the inside, which gave a 2-ft. bearing on 
all sides. The arrangement of the courses was as follows: 



296 A PRACTICAL TREATISE ON FOUNDATIONS. 

1st. A course of timbers in one length, laid transversely ; 2d, a 
course diagonally, of varying length ; 3d, another course laid 
transversely, of single length. At the top of this course a 2-in. 
shoulder was formed in the verticals ; 4th, a course laid longi- 
tudinally, resting on the shoulder ; 5th, another transverse 
course, in single lengths ; 6th, a diagonal course in varying 
lengths ; the verticals were cut off on a level with the top of 
this course. The 7th and 8th courses were transverse and of 
single length, reaching from out to out over the tops of the 
verticals. These latter were bolted by screw and drift-bolts 
to the deck-courses, as shown on the drawings. The deck- 
courses were all bedded in a good bed of cement-mortar and a 
thin grout poured into the intervals between the timbers of 
the same course ; this interval being about \ inch. Each stick 
was bolted to the course below by drift-bolts, 1 in. square or 
round, at intervals of about 5 feet. The underside of the roof 
was lined with 3-in. plank. The whole interior was then thor- 
oughly calked with oakum. This extended the full thickness 
of the plank, and when properly done the oakum compressed 
would be harder than the timber itself. The ends of all bolts 
and spikes were also covered or wrapped with oakum, the 
heads and nuts bearing hard against the oakum. The shafts, 
pipes, etc., were built into the roof, all spaces around them 
filled with mortar. In all caissons a longitudinal truss was 
constructed, resting on and fastened by iron straps and bolts 
to the end walls. This truss was about 6 feet deep, the upper 
and lower chords composed of two pieces 12 X 12 in. timbers. 
The web-members, both vertical and diagonals, were com- 
posed of timber struts, and diagonal rods 1^ in. in diameter, 
these latter extending through the first deck-course. This 
truss formed a strong stiffening rib for the roof, and also 
braces for the end-walls, and in addition affording a broad 
bearing surface for blocking or for the earthy material. Cross- 
braces were placed between the bottom chord of the truss and 
the side-walls. These were of timber, either 12X12 ins. or 
12 X 16 ins., depending upon the length required. In addi- 
tion, at each strut-brace, iron rods, 2 ins. diameter, with 



CONSTRUCTION OF PNEUMATIC CAISSONS. 297 

swivels, extended across the caisson and through the side- 
walls. Details of these rods are given in Plate XVII. 

33. This completed the caisson proper. The caissons were 
built partly on shore, supported 5 or 6 feet above the ground 
on blocks of timber. Generally only one or, at most, two 
courses of deck-timbers were placed, until the caisson was 
launched. After the interior was completed and calked, 
launching-ways were built under the caisson, and the caisson 
supported on a number of screw-jacks ; the cradles or sliding- 
ways were adjusted, the jacks lowered, so as to let the caisson 
rest on the cradles, and when everything was ready the cais- 
son was launched, then floated to its proper position, where it 
was completed. It is not necessary to put a bottom to the 
caisson when deep water is accessible ; it causes ultimate 
delay and trouble to remove it. The caissons finished as 
above described, with only 2 deck-courses, would be im- 
mersed only about 8 or 9 feet. With a good bottom, they 
would float in about 3 or 4 feet of water. Plates XIV, XVII, 
and XV, Figs. 1, 2, and 3, show details, section, and plan of 
an octagonal caisson, the interior struts radiated from a centre- 
post and rested against the sides ; the iron-rods radiated from a 
centre-collar of iron, and passed through the angles. In all 
the caissons, iron-bars, 2% X 1 in. X 8 or 10 feet, were bent 
around the angles on the outside and bolted to the timbers, 3 
or 4 straps being placed at each corner. 

34. The advantages of these forms of caissons are evident. 
The walls of the working chamber are strongly and firmly con- 
nected with the roof of the caisson, forming stout cantilevers, 
thereby relieving the pressure on the braces, as was evidenced 
by the fact that in no case were the wedges at the ends of the 
strut-braces in working chambers crushed, even under very try- 
ing circumstances, as when the air escaped suddenly from the 
caisson ; and all parts acting together local and excessive strains 
never caused any springing or leaks, nor was there any creaking 
or cracking of timbers to alarm the men. The walls of the 
working chamber are so constructed that the men had easy 
access to the cutting edge, and at the same time broad hori- 



298 A PRACTICAL TREATISE ON FOUNDATIONS. 

zontal surfaces are provided so as to obtain many square feet 
of bearing surfaces at any part of the caisson or entirely around, 
in addition to the bearing surfaces under the centre truss. 
These conditions are of great advantage in many cases. The 
caisson can be better kept level, or in case of careening can the 
more easily be brought to a level, and there is less danger of 
settling until everything is ready, as the material can be left 
under these bearing surfaces ; and in short the caisson can be 
controlled and regulated much better than when the walls of 
the working chamber are V-shaped. The latter design of 
caisson is shown in Plate XVIII, Figs. 1, 2, 3, 4, and 5. 

35. The only accident that happened during the construc- 
tion of the Susquehanna bridge was caused by the neglect of 
one of the foremen, and as much can be learned from accidents 
this one will be briefly described. The largest caisson had 
reached a point within seven feet of the rock at its highest 
point, but was twenty-eight feet above the rock at its lowest 
point. Owing to the softness of the material through which we 
were sinking, it was necessary to stop concreting in the crib to 
avoid too much weight ; the coffer-dam had been constructed 
on the crib, but had not been braced on the interior. At this 
time the top of the crib was only a few inches above the surface 
of the water ; the pockets of the crib were empty for a consid- 
erable depth. Without observing these conditions the foreman, 
being ready to sink the caisson, lowered the pressure at a time 
when the tide was at its highest. As the caisson settled the 
water raised a. few feet above the crib ; the pressure caused one 
side of the coffer-dam to be forced inwards, the water rapidly 
filling the crib and adding about 14,000,000 lbs. of weight ; the 
caisson sank suddenly until one end rested on the rock, then 
careening, settled at the other end until a sufficient bearing on 
the roof of the caisson stopped it. Seven men were in the 
chamber at the time ; they were fortunately either in the shaft 
or near to it, and ascended to a place of safety ; fortunately 
the lower door was closed at the time, and they could not enter 
the lock. The upper end of the shaft sank under the water, 
allowing the air-lock to be filled with water ; pipes were broken 



CONSTRUCTION OF PNEUMATIC CAISSONS. 299 

off, and leaks were caused in the main shafts. This air following 
the shaft made the water boil up furiously around the top of the 
lock. Four large air compressors were started at once, all pipes 
were plugged up above the surface ; and notwithstanding the 
large quantity of air that was being forced into the caisson, the 
leaks in the shafts were so great that the water was gradually 
rising. The men tore their clothes and stuffed them in the 
openings. Great difficulty was encountered in getting a dam 
around the mouth of the shaft ; but by the use of planks, tar- 
paulins, etc., the bubbling and boiling was stopped, and a dam 
of cement in bags was made, the interstices packed with oakum 
dipped in mortar. We at last were able to bail the water out of 
the lock, and the men were released, after having been confined 
in their perilous position for about eight hours. When the 
necessary repairs were made and the air again forced into the 
caisson, it was found that no leaks existed in the caisson proper ; 
that the only damage, outside of broken valves, pipes, etc., had 
occurred where the caisson had brought up hard on the rock ; 
the lower ends of the verticals had been crushed off to a height 
of about two feet around one corner of the caisson. This was of 
no moment, and the work proceeded at once The rock was 
blasted to a depth sufficient to level the caisson, which was ac- 
complished without any special trouble. We can learn from 
this, 1st. That the caisson should not be sunk until a careful 
examination is made to see that everything is ready; 2d. Al- 
ways keep the top of the main shaft well above the surface of 
the water ; 3d. Always bring the men out of the caisson before 
sinking the caisson, and 4th. The necessity of having ample 
steam-producing capacity and also reserve compressors, to sup- 
ply large quantities of air, connected up and ready for work at 
a moment's notice. Anything short of this amounts to gross 
negligence or carelessness. Air compressors are often stopped 
for a greater or less time (and men left in the chamber) for 
small repairs, want of steam, or other causes, or in case of any 
alterations in the air connections of pipes or shafts. The men 
should invariably be taken out of the caisson ; many lives have 
been lost in recent years by a failure to do so. 



300 A PRACTICAL TREATISE ON FOUNDATIONS. 

36. In some large bridges the masonry is commenced on top 
of the caisson, without using cribs or even coffer-dams ; there 
is always danger of delay and extra cost. The crib can be dis- 
pensed with, but a coffer-dam should always be constructed, as 
it is vastly cheaper to construct a dam while the work pro- 
gresses than to build one after the deck of the caisson, has dis- 
appeared under water. 

37. A crib is only necessary for rapidity of sinking, and is a 
matter of economy ; a timber or iron-cased crib will not cost 
more than one half to one third that of masonry per cubic 
yard ; the crib can be built up rapidly and with relatively small 
expense in calking will be sufficently water-tight ; occasional 
bailing or pumping will keep the leaks down. A crib of this 
kind is really a solid single-wall coffer-dam, well braced on the 
interior. 

Sometimes cribs are built open, leaving 12 -in. spaces 
between the courses of timbers ; the transverse braces passing 
between the courses having likewise 12-in. spaces between them. 
There is no economy in this, as the spaces are to be filled 
with concrete (see Plate XVIII). As water circulates freely in 
the crib, much of the concrete will either have to be placed 
under water or subjected to the action of the water before it 
has had time to set, preventing sound, solid work and causing 
waste of good material. The work cannot be altogether sat- 
isfactory, and as the concrete should be packed under and 
between the cross-timbers, hollow spaces will necessarily exist. 
This can be avoided largely by using round logs, stripped of 
bark, for the cross-braces ; they are equally as good, and would 
cost somewhat less than braces sawed square. A crib thus 
constructed practically divides the mass of concrete into iso- 
lated prisms or columns of concrete. 

Solid walls, either calked or not, are used with solid or open- 
work cross-walls, or braces ; the same objections occur in this 
case, so far as isolating the columns of concrete. 

In the cribs used in the structures now being described, 
both of these objections were to a great extent removed. The 
outside walls were built solid and calked ; the cross-walls were 



CONSTRUCTION OF PNEUMATIC CAISSONS. 3OI 

built solid for a few courses of a height one third or one 
fourth that of the crib. The positions of the cross-walls were 
then shifted to the middle of the pockets below, and built up 
solid for a like height, then shifted vertically over the lower 
walls, and so on alternating 2 and 3, and 3 and 4 in number. 
In this case it was only necessary to pack the concrete under a 
few timbers, which could be cut on a bevel or be round ; the 
various columns of concrete were consolidated into practically 
a homogeneous and united mass. The water could be kept 
from any layer as long as desired. The side-walls were dove- 
tailed at the corners, and the cross-walls were dovetailed into 
the timbers of the outside walls. All timbers were drift-bolted 
together with i-in. round or square bolts 22 ins. long, spaced 
about 5 ft. intervals — the courses of timber breaking joints. 
These cribs were planked on the outside, the plank placed ver- 
tically in lengths of 5 to 7 ft. and spiked ; this kept the calk- 
ing in place — otherwise of no special advantage. At the 5th or 
6th course of timber from the top, iron bolts 2-ins. diameter, 
with a large eye on one end, were placed through the outer 
walls of the crib ; these were for connecting the vertical rods of 
the coffer-dam. Drawings, Plate XIII, fully illustrate the con- 
struction of the cribs ; these were square-ended. Pointed-end 
cribs can easily be constructed when desired, and should be 
pointed, if they extend near to the surface of the water, so as 
not to obstruct the current too much (see Plate XIX). The 
tops of these cribs were from 15 to 30 or more feet below low- 
water, and did no justifythe additional amount of material and 
costs as it would have also necessitated longer caissons and con- 
siderable extra expense in the sinking. 

38. The design of coffer-dams used was simple, strong, and 
efficient. When the height required was over 20 ft., they were 
built in two sections similar in every respect to each other. A 
12 X 12 in. sill was placed on the walls of the crib, overlapping it 
by 3 ins. on the inside. Vertical pieces 12X12 ins. were erected 
on these at intervals of 4 or 5 ft., connected with the sill by 
mortise and tenon, and then caps mortised and tenoned to 
them ; cross-pieces placed across the top projected outward 



302 A PRACTICAL TREATISE ON FOUNDATIONS. 

over the iron eye-bolts in the crib and long iron rods 2 ins. 
diameter with hooks at one end and threads at the othe-r were 
hooked to the eye-bolts and passed through holes in the cross- 
pieces, on the upper ends thimbles or sleeves with right and 
left hand threads were screwed, pressing the coffer-dam hard 
to the crib. The sleeves were used instead of nuts, so as to 
connect other rods for the upper sections of the dams ; the 
usual nuts were used on the top of these bolts. A double 
course of 3-in. plank was then spiked to the uprights — the first 
or inner course laid diagonally, and the outer horizontal for 
convenience of calking ; the entire outside was well calked. 
Two tiers of braces on the inside were sufficient for a section 20 
ft. high ; strong cleats were spiked to the cross-walls of the crib 
to brace the bottom sills. Plans, sections, and details are shown 
in Plates IV, Figs. 1 and 2, and XIII, Figs. 1, 2, and 4. The 
upper section was constructed in the same manner. This con- 
struction answers well for heights from 40 to 45 ft. The octag- 
onal cribs and coffer-dams are different only in the struts and 
rods for bracing which radiate from centre-posts. The corner- 
posts of all dams were made in two pieces, and bolted together ; 
when these bolts were removed and the iron rods unhooked, 
the sides and ends were free to separate. It was intended to 
use these on other cribs, but it did not prove either economi- 
cal or practicable. The only coffer-dam that gave away was 
caused by the accident already explained. 

Plate XVIII, Figs. 1, 2, and 3, shows another form of 
caisson, crib, etc., often used, open-wall cribs being employed. 

Article L. 

CAISSON SINKING. 

39. THE construction of the caissons, air-locks, size, and 
kind of pipes, machinery, connections, etc., having been 
described, it only remains to explain briefly the methods used 
in excavation, sinking caissons, and filling the working chamber 
with concrete. It may be stated that in general all materials 
that are too large to pass out through the pipes have to be 



CAISSON SINKING. 303 

carried out through the main shaft in buckets or bags. There 
are patent buckets, which slide through a shaft left in the 
caisson, being raised or lowered by machinery. When the 
bucket is lowered into the working chambers by the proper 
adjustment of valves and pipes, doors can be opened into the 
working chamber, large bowlders, sticks of wood, and other 
debris can be thrown into the bucket, the doors closed, air 
pressures equalized, and the bucket with its load lifted out. 
The arrangement is simple and efficient, but has never been 
generally adopted. In the writer's experience the larger 
bowlders and pieces of crushed rock were generally piled on plat- 
forms resting on the truss and braces and carried down with 
the caisson, mainly removing from the interior the sand, 
gravel, etc. The bowlders were ultimately used in the concrete 
or rubble-work in the chamber. There are some objections to 
this, as the men are inconvenienced in moving about, and have 
to work under heavily loaded platforms, which involve-s 
some danger. It causes some delay and expense, but on the 
whole is probably more economical than breaking up the 
bowlders, removing them from the caissons, and again putting 
them back in the form of concrete. • 

40. The removal of the sand, gravel, and mud can be ef- 
fected by the sand pump, mud pump, or by the blowing-out 
process, each of which will be briefly described. As has been 
mentioned, a number of discharge pipes were built into the 
caisson, extending through the deck. Sections of pipe 8 or 9 
ft. long are screwed on to these at the bottom, reaching down 
into the material, the lower end bent at right angles. A small 
wooden paddle is pressed against the end by the air when the 
valve is open ; the material excavated is shovelled in a pile 
around the lower end of the pipe ; when the paddle is removed 
the air forces the material up and through the pipe with great 
force. At the top an elbow or goose-neck of chilled iron two 
or three inches thick is fastened. This discharges the ma- 
terial outward and downward. These elbows are rapidly cut 
through by the sand and gravel, requiring frequent renewals. 

For details of shafts, air-locks, pipes, etc., see Plate XX. 



304 



.-/ PRACTICAL TREATISE ON FOUNDATIONS. 



The process is simple, but requires great care in feeding the 
material to the pipe to prevent its choking up. A dense fog al- 
ways sets up when the pressure is lowered, and often water rises 
in the caisson, and much air is used, taxing the air compressors 
greatly. Notwithstanding these objections it is largely used. 

41. The mud pump and sand pump do not differ materially 
in design, nor at all in principle. The mud pump will be 
alone described. It consists of a pear-shaped cast-iron vessel 
about 15 ins. in diameter and length, which has a hemispherical 
lining, a a, connected with the top; also 
three openings into it./', r, and d, to which 
hose or pipes can be connected, bg is 
called the suction pipe, ck the supply 
pipe, and dk the discharge pipe, bg is a 
long hose, so as to be moved freely about ; 
its lower end has an iron strainer to pre- 
vent any large material or sticks, etc.. en- 
tering. Its upper end is screwed into the 
bell and has a hollow, conical-shaped point, 
which reaches into the neck of the dis-' 
charge pipe, which also tapers slightly, so 
that the annular space between the two 
can be either widened or narrowed. Water 
is forced by a large pump down through 
the supply pipe, and impinging on the iron -^^^^^^^ 
lining is scattered around it. and then ' Fl ^^_ MrP0R SAN , Pn , r 

passes upward through the annular space, for Removing Material from 
, . , " ,. , . ,. Working Chambers of Pneu- 

and upward in the discharge pipe, ate. MAT1C Caissons. 

This creates a partial vacuum at the end of 

the supply pipe. The sand, mud, and water are thus drawn up 

into the discharge pipe, and are discharged at the top. A large 

quantity of material can thus be removed without decreasing 

the air-pressure, but the material is required to be cut up 

fine and mixed with water.* 




* The Monson sand-pump has a vertical section almost oval is made of 
cast iron with wrought-iron bands, horizontal section is nearly circular. The 
supply-pipe enters the pump near the bottom; there is no inner lining, other- 
wise the design and construction is similar to the above-described mud-pump. 



CAISSON SINKING. 305 

42. In making the excavation, the material should not be 
removed from under the shoulders until the middle space has 
been excavated to the depth of 2 or more feet below the cut- 
ting-edge, so as not to leave the caisson unsupported for any 
great length of time, and not at all under the lower side, if 
the caisson is out of level. When everything is ready, the men 
should be brought out and the caisson lowered by gradually 
reducing the pressure. When the resistance to lowering is very 
great, requiring a great reduction of pressure, one man gener- 
ally remains in to see if any serious leaks occur or any great 
inflow of material takes place, so as to signal for the pressure 
to be put on. He could readily ascend the shaft if necessary. 

43. As has been stated, the borings indicated a very great 
difference of level in the rock-bed, being from 15 to 20 ft. in 
the length of the caisson in some instances, and that blasting 
from the surface had proved impracticable at any reasonable 
cost. During the sinking, as the caisson approached the high- 
est part of the rock, constant soundings were made with an 
iron rod, to avoid the danger of coming suddenly on the rock 
at any point, and when the highest point of rock was reached 
our principal difficulties commenced. There was but two 
courses open : either to blast the rock and sink the caisson to 
the level of the lowest point of the rock, or to hold the caisson 
where it was and carry on the excavation below the cutting- 
edge, then build up with concrete under the caisson, and 
then fill the working chamber. The latter plan was adopted, 
as the rock was very hard and only small charges could be 
used, which would have required a long time and added enor- 
mously to the cost of the work. The great danger in excavat- 
ing below the cutting-edge arose from the fear of the caisson 
careening and settling out of level. This danger was obviated, 
however, by cleaning out sections of about 10 ft. square, one 
at a time, leaving the rest of the caisson well supported. The 
rock at the bottom of these pits, if sloping, was blasted to an 
irregular surface, forming depressions and elevations. The 
concreting was then commenced and carried up to the cutting- 
edge and packed under the shoulders. Another section was 



306 A PRACTICAL TREATISE ON FOUNDATIONS. 

then completed in a similar manner. Where the depth to the 
rock did not exceed 5 or 6 ft. no trouble arose ; but in greater 
depths the material under and outside the cutting-edge would 
cave in, endangering the safety of the caisson by a sudden 
escape of the compressed air, called " blow-outs." This would 
frequently happen in sand and gravel, but seldom in clay or 
silt. To avoid this difficult}' the pits were lined with frames 
and sheeting, as in sinking shafts into the ground. These tim- 
bers had to be cut of the proper lengths and carried, one by 
one, down the shaft; but by this means pits 12 to 15 ft. deep 
were sunk and filled with concrete. In sand and gravel it was 
often impossible to hold the material, and the framing or 
bulkheads would break in, followed by much inflow of the 
material and escape of the air, but, gaining little by little, the 
entire side would sooner or later be sealed up. This difficulty 
in sand and gravel arises from the fact that the pressure can- 
not be kept up greater than that due to the depth of the cut- 
ting-edge below the surface of the water, as the escape of the 
air is so great. In clay or silt the material itself is air-tight or 
nearly so at that depth, and the pressure can be raised to 
almost any extent. Caving in also occurred in this material 
to some extent when unsupported, but it could be easily held in 
place. In the case of the caisson to which the accident hap- 
pened, as already described, we were compelled to blast the 
rock to a depth of about 7 ft. around a part of the caisson in 
order to level it. This still left about 13 ft. to be excavated 
below the cutting-edge at the other parts, which was done as 
above described. Having in this manner constructed a wall of 
concrete entirely around the caisson, the material enclosed was 
then removed. Blasts were put in all the sloping surfaces, 
bringing the entire surfaces to a series of depressions and rises 
in both directions, in order to prevent any danger of sliding. 
No attempt, however, was made to cut the rock to a level 
or even to a series of steps, the surface being simply very 
much roughened. Some engineers have drilled large holes in 
the rock and inserted iron rods projecting a foot or more above 
the rock in order to prevent sliding. 



CAISSON SINKING. 307 

44. The filling of the air-chamber with concrete was then 
proceeded with. All the concrete was mixed in batches, using 
about a barrel of cement to the batch. This was mixed by 
hand on a platform above and was passed through the supply- 
shaft, which was simply a long air-lock formed by a door at 
top and bottom. When the signal was given the concrete was 
mixed and immediately shovelled into the shaft, the lower door 
being closed and further supported by a timber strut. When 
a sufficient quantity had been thrown in — from \ to 1 cubic 
yard — the upper door was closed, the air equalized, and the 
lower door opened, the concrete dropping on a platform. It 
was then carried in barrows, deposited in place, and rammed. 
Before throwing the concrete into the shaft several buckets 
of water were thrown in, and also after throwing the concrete 
in. The water prevented the cement from adhering to the 
shaft and from heating and setting too rapidly when the com- 
pressed air entered the shaft ; otherwise the shaft would be 
blocked, and it would be difficult to clear it again. The hot 
air of the chamber, unless a plenty of water is used, causes the 
cement to set before it can be properly handled. It requires 
great care and a concrete rather dry and mixed with very 
small chips of stone to pack close against the deck of the 
caisson. It is better to leave one or two sections of shaft in 
place. The upper sections can be removed and used over 
again. 

45. There is nothing of special note in the Schuylkill River 
caissons except their great length as compared with the width, 
which was required by the line crossing the stream very ob- 
liquely. The abutment caisson was nearly square. No crib was 
used, but a high coffer-dam was constructed on the caisson : this 
was filled solid with rubble masonry, one man stone bedded in 
concrete ; the air chamber was filled with concrete. As this 
caisson had to support the thrust of a heavy mass of earth 
resting on the swamp, timber strut braces and large iron tie- 
rods were used in the working chamber to prevent sliding, and 
the bed was given a slight slope against the direction of the 
pressure. (Plate XVI, Figs. 1, 2, and 3.) 



308 A PRACTICAL TREATISE ON FOUNDATIONS. 

46. The points especially worthy of notice in the Tombig- 
bee River bridge was the nature of the material on which the 
structure was built, and an accident that happened to one of 
caissons, from which some useful information can be obtained. 

The site of the bridge was inaccessible ; the river itself being 
the only avenue for transportation, and this alternating between 
extreme high and low water. All materials except timber had 
to be transported long distances. Brick and shells were used in 
the concrete. The material underlying the water was a shifting 
sand, resting on a silt intermixed with irregular bowlders, or 
broken layers of a bluish-white marl. There was 23 ft. of water 
at the lowest stage; but sudden rises of 35 to 40 ft. often oc- 
curred, and at irregular and uncertain periods. A simple crib or 
open caisson, resting on the bed of the river, would inevitably 
have scoured out ; nor could piles be relied upon, as owing to 
the irregular layer of marl, through which they could not be 
driven, some would have scoured out. A coffer-dam would 
have been required of great height, and liable at any time to be 
scoured out or flooded ; and in addition, the varying depths 
of the borings left it uncertain as to the proper depth at which 
the structure should be founded. For these reasons the writer 
determined to sink pneumatic caissons, as then all doubts and 
difficulties could be settled at the proper time. The octagonal 
caisson was sunk through 23 feet of water, 9 feet of sand, silt, 
and patches of marl, and the excavation carried about 9 feet 
below the cutting-edge in silt. It was found .impracticable to 
sink the caissons farther, although the entire air-pressure was 
let out of the caisson. This indicated an unusual frictional re- 
sistance on the outside ; doubtless due to the marl bowlders 
bearing strongly against the sides of the caisson. The pier, 
however, at this time was only about one half completed ; but 
with this large and well-defined frictional resistance, and the 
fact that borings indicated an almost unfathomable depth of 
silt below, it was determined to build at that point. The cais- 
son was filled with concrete resting on the silt ; this material was 
so soft that a rod four or six feet long could be readily pressed 
into the material. The writer's experience with driving piles, 



CAISSON SINKING. 



309 



and their great bearing capacity in that kind of material, to- 
gether with the fact that on the same river screw-pile piers 
constructed by him, having only 100 sq. ft. bearing to the pier 
and carrying spans 150 ft. long, carrying the heavy loads of the 
present day, had stood for nearly twenty years, gave confidence, 
as this pier would have fully 1000 sq. feet of bearing, although 
it would carry heavier piers and longer spans. The weight at 
the time the caisson was stopped was 1,684,500 lbs. ; and as the 
caisson did not rest on anything at the bottom, the entire cut- 
ting-edge being cleared in order to sink the caisson, if possible, 
and the air-pressure entirely relieved, it was a clear case of 
balance by friction. And as the exposed surface was 1200 sq. 
ft. the frictional resistance must have been 1400 lbs. per square 
foot. Then concrete was packed under the cutting-edge and 
shoulders on the lower side, and the pressure again lowered ; 
the weight now acting with a lever-arm of about 10 feet. The 
frictional resistance on about one half of the exposed surface 
would be acting with an arm of about 20 feet or more. But 
the caisson did not settle a particle ; this seemed to be conclu- 
sive as to the ultimate bearing of the foundation. The com- 
pleted structure, including the rolling load on the bridge, weighed 
4,374>5°° lbs. ; area of base of caisson, 1 148 sq. feet ; bearing 
resistance of foundation-bed, not considering any allowance for 
friction = 3810 per sq. ft.; and allowing 1,684,500 lbs. for fric- 
tional resistance, the pressure on the silt is 2343 lbs. per sq. ft. 
This is not an unusual pressure for this material, as seen in 
paragraph 306, Part I, Table No. 6. 

This is particularly mentioned as a safe load at that depth, 
on the softest material that can be called solid or earth. This 
bridge has been in use now for over six years. The piers were 
built of brick, and carry 275-ft. spans. Such spans on brick 
piers are somewhat unusual. The brick was hard, sound, well 
burnt, and laid in cement mortar. 

47. One of the rectangular caissons 45 X 23 ft. X 14 ft., 
with a crib 20 ft. high, partly filled with concrete weighing 800 
tons, simply resting on the bottom, was lifted by the water in 
a rapid rise of the river ; and although well secured to a num- 



310 A PRACTICAL TREATISE ON FOUNDATIONS. 

ber of clusters of piles driven around it, and swung askew of 
its proper position and dropped 10 ft. down stream, it could 
not be pulled back into position against the current, and had 
to be flooded where it was. Sinking somewhat suddenly, the 
material at the upper end was scoured out ; this swinging in- 
stantaneously into the eddy under and at the down-stream end 
collected into a mound, and when the flood subsided the cais- 
son was found in an inclined position at an angle of about 35 
or 40 . A contract was made with parties accustomed to 
lighter vessels across the bar below Mobile to lift the caisson 
into position. The first difficulty was in getting chains under 
it. This, however, was ultimately accomplished, the lighters 
lowered, necessary connections made, the water pumped out ; 
but the caisson did not lift, the largest iron chains snapping 
and breaking. Failing in this the concrete was blasted out of 
the crib ; the caisson did not float until air connections were 
made and air-pressure put on, when it rose suddenly. It was 
then located and the work proceeded to a finish as usual, but 
many thousands of dollars had then been wasted. 

The first lesson to be learned from this accident is that it is 
unwise to attempt to resist the action of such rapid and high 
rises in rivers. Had this crib been flooded in the earlier stages 
of the rise, and had we waited patiently for the fall of the river, 
both time and money would have been saved; and, second, it is 
a waste of time and money to endeavor to lift such structures in 
place. It is far better to lighten the load, and let natural laws 
and forces aid in the floating of the structure.* 

From the contract prices paid on this work, which were 
$42.00 per 1000 ft. B. M. of timber, $10.00 per cubic yard for 
concrete in crib, and $15.00 for concrete in caisson, 5 cts. per lb. 
for iron, and 20 cts. per cubic foot of excavation sinking cais- 
sons, the cost of the work below water would be $15.06 per 
cubic yard. The actual cost, taking in consideration accidents, 
delays, and loss of material, was considerably greater. 

* It is but justice to say that Mr. H. F. Lofland, the Div. Engineer in charge 
of the bridge, earnestly pressed the importance of flooding the caisson in time 
to have saved it, but unwise counsels prevailed, and it was not flooded until too 
late — a valuable but expensive experience. 



COMBINED OPEN-CRIB AND PNEUMATIC CAISSON. 3 II 

Article LI. 
COMBINED OPEN-CRIB AND PNEUMATIC CAISSON. 

48. As was mentioned, the writer designed a combined 
structure for the purpose of reaching rapidly, economically, 
and certainly a depth beyond that at which the pneumatic 
caisson can be sunk, upon which he secured a patent. This 
structure will now be described, both on account of its being in 
its general design typical of both the general construction of 
a timber or iron caisson, and of the novel features making it 
available for use as a pneumatic caisson, or an open crib. 

The description will be better understood by referring to 
Plates XI and XII, Figs. 1, 2, 3, and 4. As a crib, the descrip- 
tion already given will suffice (see paragraphs 2, 3, 4, Art. 48, 
Part Third). 

As a caisson it may be stated in general terms that there are 
one or more decks or roofs, converting that portion of the crib be- 
low into a caisson ; these roofs are removable in part or entirely. 
As many separate and distinct air-locks as may be desired or 
required can be introduced. An iron shaft can be extended 
throughout the entire height of the crib ; any part of this shaft 
or its entire length can be converted into an air-lock. Piles of 
50 ft. or more can be introduced into the air chamber and 
driven below the lower edge of the caisson. The general ad- 
vantages secured are that, 1st. To the depth of a hundred feet, 
or whatever may be the limit of the pneumatic process, we se- 
cure the advantages attaching to this process. 2d. That be- 
low this depth the structure can be used as an open crib, sunk 
by the usual methods, securing a minimum vertical lift of the 
dredged material, — a largely reduced frictional resistance on the 
outside surface, thereby enabling greater depths to be reached 
than in any other manner more rapidly and at less cost. And, 
3d, should for any reason the crib be stopped by any obstruc- 
tion, long piles can be introduced and driven until a satisfactory 
bearing is obtained. 4th. It is specially applicable in very 
great depths of water where the bed of the stream has not 



312 A PRACTICAL TREATISE ON FOUNDATIONS. 

bearing resistance sufficient to build upon it, and where the 
excessive lift of the dredged material would greatly increase 
the cost of construction. 5th. It provides those conditions 
and means of, to a great extent, removing the injurious effects 
resulting from working in compressed air, adding to the com- 
fort and health of the men, without obstructing or delaying 
the prosecution of the work, and adding but little to the cost 
of the structure itself. 6th. For small depths, after sinking as 
a pneumatic caisson, the roof can be removed, after partly or 
entirely filling the air-chamber with concrete, by which a solid 
and uniform mass of concrete or masonry can be built from 
bottom to top of the piers. 

49. Fig. 1, Plate XI, is a vertical cross-section, showing 
double walls of crib and cross-walls A, which are to be 
filled with gravel or concrete, which furnishes the weight nec- 
essary to sink the caisson and also forming a part of the per- 
manent foundation. As seen in the drawing, V-shaped cutting- 
edges are formed and built solid for a height of about 9 ft., 
through which both screw and drift bolts are passed, and all of 
the walls tied together with long iron rods. From that height 
the several walls are formed by 12 X 12 in. timbers laid on top 
of each other and drift-bolted ; cross-braces at intervals tie the 
walls together. These walls are built up as the caisson sinks; 
the extreme outside walls are built with a gentle batter, or the 
lower section alone may have a batter, and all above vertical : 
this latter is common, especially when iron is used. The parti- 
tions C from wall to wall constitute the various roofs, dividing 
the space between the walls into a number of chambers 8 or 9 
ft. high, marked B in the drawing. The entire outside and 
also the roofs are calked or otherwise made air-tight. Air- 
locks D built into the roofs afford means of passing from 
chamber to chamber. In the middle space an iron shaft ex- 
tends from top to bottom, any part of which or the entire shaft 
can be converted into an air-lock. These shafts communicate 
by side-doors with the chambers. An air-pressure due to the 
depth can be maintained in the chambers, the difference of 
pressure in the successive chambers being that due to the 
height of the chambers. Any number of roofs may be used. 



COMBINED OP EN- CRIB AND PNEUMATIC CAISSON. 313 

The roofs in the middle space are constructed with iron beams 
and plates riveted to them ; those in the two outside spaces 
are shown with a timber construction. Also air-locks D' afford 
a communication from the chambers to the spaces between 
the walls, an open vertical shaft being left in the concrete ; 
the men having the choice of entering or leaving the caisson 
by this avenue, this twofold avenue increasing the chances 
of escape in case of accidents. The usual air, water, and 
discharge pipes, P, are shown. The drawings show some of 
the air-locks in section, others in elevation. The doors are 
shown both while open and closed. Fig. 2 is a horizontal sec- 
tion showing the roofs partly removed ; B, chambers ; C, roofs; 
D, air-locks and shafts. As the roof may be formed of iron 
beams and plates, the roofs can be opened by removing the 
plates, leaving the girders to serve as braces; or, as shown at T, 
the plates under two of the girders can be left in place, thereby 
forming troughs into which the dredged material can be emp- 
tied, and discharged by the air through pipes. The proper 
spaces are shown partly filled with concrete in both drawings. 
Figs. 3 and 4 are part sections, the first showing the method of 
introducing piles into the caisson through long air-locks and at 
the bottom piles driven and partly filled over with concrete. 
Fig. 4 shows the caisson sunk below the limit of the pneumatic 
process, in which the lower roof C has been removed except as 
to necessary bracing ; this roof just passing below the water 
surface, the roof C is as yet intact. 

Object and Uses of the Above Structure. 

50. Assuming a depth of water, say 100 ft., underlaid by a 
soft, silty material, into which piles can be easily driven thereby 
securing a sufficient support. A caisson of this kind could be 
sunk resting on the bed of the river. Piles could then be in- 
troduced after the air-pressure was established, as shown in 
Fig. 3, and driven to the required resistance, cut off squared, 
capped if desired, and then concrete built over them to any de- 
sired height, and the masonry then commenced. The ma- 
sonry, if desired, could be commenced on top of the piles. 



314 A PRACTICAL TREATISE ON FOUNDATIONS. 

This evidently furnishes an economical mode of securing a 
foundation where the depth of the water is great and the un- 
derlying material uncertain. 

The crib resting on the bottom at, above, or below the 
limit of the pneumatic process, with the roof C at this level, 
the roof C could be partly removed, leaving the trough-shaped 
braces in place ; the material, dredged and lifted into this 
trough, could be discharged, either by the air-pressure or mud 
pump, through proper discharge pipes. As the caisson sinks, 
the roof c reaching the water surface, the roof C could 
then be partly removed; the men using this as a platform 
from which to work. BB„ then being the work chamber, 
B 2 passing below the water surface gradually. When C 
reaches the limit, the men ascend to C v and so on. These 
operations are indicated in Fig. 4. In this manner we make 
use of the pneumatic pressure as far as practicable. We 
limit the lift of the dredged material to a minimum, and se- 
cure the advantage of the rapid and economical methods of 
removing the material adopted in ordinary caissons. The 
water is kept at a constant level, the men ascending as the 
caisson sinks. In addition, the air escaping under the cutting- 
edges and rising along the sides reduces materially the resist- 
ance of friction by loosening the material. There can be 
no doubt that this process is reliable, expeditious, and economi- 
cal, and can be used where other means would fail. If the depth 
should be 200 ft. below the water surface, say 70 feet water 
and 130 ft. solid material, sink the caisson by the pneumatic 
process 100 ft. At this point the dredging would commence, 
the lift gradually increasing from o to 100 ft., or an average 
lift of 50 ft., the air or the pump doing the balance. In the 
open-crib process the dredging would commence, when the 
caisson rested on the bed of the river, the first height of lift 
being 70 ft., gradually increasing to 200 ft., the average lift 
being 135 ft. It is perfectly evident that this method must be 
slower, more expensive, and more uncertain. 

51. The construction is by no means a bad one for a cais- 
son to be sunk less than 100 ft., or for an ordinary caisson. 



COMBINED OP EN- CRIB AND PNEUMATIC CAISSON. 315 

It would not require, before commencing to sink the caisson, 
the delay necessarily caused by the time required to construct 
the ordinary caisson proper. The heavy mass of timber re- 
quired in the roof would, to a large extent, be avoided. Only 
one roof would be necessary in this case ; but it would be ad- 
visable to use at least two, the chamber between being used 
for a dressing and warming room for the caisson men, through 
which they could pass as leisurely and as comfortably as may 
be desired, without obstructing in any manner the progress of 
the work. It is evident that the roofs should be of iron, as it 
can be more conveniently constructed and removed. It has 
the further advantage that, in case it should be found neces- 
sary after sinking the caisson to go beyond the pneumatic 
limit, additional roofs could be constructed and the sinking 
continued, or piles introduced and driven ; whereas, in the 
pneumatic caisson proper, when its limit is reached, it can 
neither be sunk further nor removed ; and it is possible that r 
under such circumstances, the structure would be useless, its 
entire cost thrown away, or an uncertain foundation used. 

52. The entire structure can be built either of iron or wood, 
the choice being mainly one of cost, as the strength in either 
case is sufficient, or the part below the bed of the river could 
be wood and the part above of iron — especially if in sea water, 
where the timber would be destroyed by worms, and also 
where obstruction to the current or navigation is a matter of 
moment, somewhat less space would be occupied by the iron 
wall. In short, the writer does not hesitate to say that it is a 
good design for any kind of foundation below water for any 
depth of water or solid material from 30 to 200 ft. It has, 
however, its special application in those rivers, such as the 
Mississippi, at New Orleans, where there is a great depth of 
water, and where any such obstruction to the channel would 
be bitterly opposed, as the structure could be narrowed to a 
minimum thickness at any desired depth below the water sur- 
face, without in any manner interfering with the prosecution 
of the work below. " It is claimed in the patent that greater 
depths can be reached than by any other known method, and 



3l6 A PRACTICAL TREATISE ON FOUNDATIONS. 

at any depth the work can be done relatively more rapidly, 
more economically, and more certainly, and that for such 
depths as require only the ordinary coffer-dam absolute se- 
curity against breaks and leaks can be secured, and founda- 
tions can be constructed either under a moderate pressure, or 
after fully bracing and sealing up the cutting-edge the roof 
can be removed, and the work proceeded with safely and se- 
curely, as in an ordinary coffer-dam in the open air." See 
Plates XI and XII. 

In the year 1889 the writer showed Mr. E. L. Corthell, an en- 
gineer of great ability and experience, the plans and descriptions. 
He was then working on the Memphis Bridge Plans. It had 
been supposed by many that the depths required for that bridge 
would be much greater than was afterward found necessary. 

In 1890 Mr. Corthell made a report on building a bridge 
across the Mississippi, near New Orleans, and in this report he 
recommended the above plan. 

GENERAL REMARKS. 

53. In all of the foregoing subjects the writer has de- 
scribed, in general terms, the actual methods of the construction 
of caissons, cribs, and coffer-dams, etc., as practised by himself 
and many other engineers, and also the subsequent operations 
of sinking, with more or less detail, without criticism of the 
methods of others. He has, however, often alluded to the 
importance of avoiding, as far as practicable, the adoption of 
what seemed to be useless refinement in the sizes and quan- 
tities of materials used in such structures, as well as in the 
manner of putting the parts together, necessitating increased 
cost and time required in construction. And in all designs his 
aim has been to keep in view that good engineering practice 
only requires that all structures should be constructed in the 
least possible time, and the least possible cost, consistent with 
strength, durability, permanency, and suitableness to the end in 
view. That this does not seem to be the practice of many 
engineers is apparent in many structures and in many portions 
of the same structure, and as they do not generally result in 



COMBINED OPEN-CRIB AND PNEUMATIC CAISSON. 317 

any better work and only add to the time and cost, such prac- 
tice can only be considered useless and wasteful of both time 
and money. Attention to some extent was called to this sub- 
ject in discussing the subjects of concrete and masonry, and 
the effort was there made to show in what manner first-class 
work in every respect could be secured without useless and 
onerous requirements such as are often imposed. Attention 
will now be directed to similar requirements often imposed in 
the construction of some deep and difficult foundations. 

It is not uncommon to see described in books for the con- 
struction of the sides of open caissons, which are simply timber 
coffer-dams, that they should be composed of planed and 
tongue and grooved timbers, sometimes of specially large 
cross-sections, where as timber as it comes from the mill is in 
every respect as good, no planing being necessary, except pos- 
sibly planing slightly the edges of the outside plank for a 
calking joint. 

The guide-piles of coffer-dams are often required to be 
sawed square. Round piles are equally as good, cost less, and 
can be driven much more satisfactorily. In framing cribs that 
are to be filled with concrete, it is far better to use round logs 
for the cross braces, any slight variation in the diameter at 
the two ends being a matter of little or no moment, and 
they admit packing under and around them to much greater 
advantage. And in many cases the entire crib could be con- 
structed of round logs without in any way impairing the use- 
fulness of the structure, as for many purposes under water sap 
wood is as serviceable as heart wood. 

In the construction of the pneumatic caisson particularly 
there seems to be no regard paid, as a rule, either as to the 
cost or to the relative strength of the parts ; bolts and rods are 
inserted \% large quantities where there would seem to be little 
or no use for them ; and no special attention is given to a strong 
and rigid connection between the walls of the working cham- 
ber and deck of the caisson, which is matter of the greatest 
importance. For instance, in the deck of the caisson com- 
posed of eight or ten courses of timber crossing each other, 



31$ A PRACTICAL TREATISE ON FOUNDATIONS. 

drift-bolts I in. X 22 ins. are driven at every intersection ; this 
would require in any ordinary-sized caisson some 32,000 drift- 
bolts, or about 190,000 lbs., costing some $8000 to $io,coo, 
when one fourth to one fifth of these quantities would be 
ample under any circumstances ; and in addition long bolts 
1^ to 2 ins. and 8 or 10 ft. long are put through the entire deck 
with a reckless profusion, and only to hold timbers together 
that have little tendency to separate ; and similarly in other 
parts, except that comparatively few bolts are used to connect 
the deck to the walls of the air-chamber, where the danger 
really exists, and where the framing is usually such that, out- 
side of the interior bracing, the bolts are the only connections. 
Often, also, in constructing caissons, all of the timbers are run 
through a planer, so as to gauge them to exactly the same size. 
Surely nothing is gained by this ; the cost, however, is greatly 
increased. Unless the timber is badly sawed, an equally good, 
if not better, work is secured by bedding the timber in cement 
mortar, and filling the vertical joints with grout. In regard to 
incasing the cutting edge of a caisson in iron plating, there is 
much difference of opinion and practice. It can safely be said 
that it is not necessary ; it may be a safe precaution, and it 
may or may not add materially to the cost. It is claimed by 
some engineers as a decided disadvantage. The writer has 
never used it. 

Often expensive stagings and platforms are erected to 
regulate and control the sinking of caissons : here again the 
writer cannot speak from experience ; they will certainly be 
very costly, and their utility is certainly doubtful. The writer 
only used a few clusters of piles, mainly to hold the caisson 
while floating, and to aid in locating the caisson accurately qn 
the bottom, no material error in position resulting during the 
sinking. Tendencies to move gradually in one direction are 
sometimes developed, which can generally be checked either 
by blowing the material to that side, or by settling the caisson 
slightly out of level, and then levelling it again ; reasonable care 
and watchfulness will ordinarily prevent any trouble. Many 
such matters do not, of course, admit of any close calculation, 



COMBINED OPEN-CRIB AND PNEUMATIC CAISSON. 319 

and for this reason it is the aim to be always on the safe side, 
which is commendable so far as it applies ; but there is nothing 
gained by enormously strengthening some parts of a structure 
and leaving other parts proportionately weak. The writer's 
object is only to call attention to some of the evidently useless 
waste of material, money, and time, without any reasonably 
compensating advantages. Spare no time or money in strength- 
ening weak points, but do not waste them on those essentially 
strong points, that can take care of themselves. 

The writer made estimates for contractors proposing to 
build a large caisson and sink the same under specifications 
which fully illustrates the above remarks. A few extracts will 
be given for the corner-posts : 

4 pieces of white oak, 24 ins. x 24 ins. X 16 feet. 

4 " " " 16 ins. X 27 ins. X 16 feet. 

312 " " " 12 ins. x 16 ins. X 16 feet. 

The other timbers for the caisson were of almost all con- 
ceivable dimensions : 12 in. X 12 in. X 20 feet, 12 in. X 12 in.X 
10 ft. 2 in., 8 in. X 12 in. X 17 feet, and so on ; in all 908,616 ft. 
B. M., every stick of which had to be planed. The writer does 
not hesitate to assert that an equally strong, durable, and 
rigid structure could have been built with no variations in di- 
mensions from 12 ins. X 12 ins., except in the lengths of certain 
parts which have necessarily to be specified ; and further, that 
the planing of the timbers was absolutely without necessity 
or even advantage. Pine timbers would have been equally 
suitable. Such requirements simply mean an enormous waste 
of money and time. In addition, screw-bolts amounting to 
43,000 lbs., in all lengths from 2 to I2| ft., and from 1 to 2\ 
ins. diameter, were stuck in all conceivable places through the 
deck of the caissons, through corner-posts, etc., and in addition 
1992 drift-bolts \\ in. diameter and 58,348 drift-bolts 1 in. diam- 
eter, amounting in the aggregate to 350,623 lbs.; these were 
used at every intersection in the deck, that is, one foot apart 
in each direction over each of the seven crosses of solid timber 
in the deck. Whereas one fifth of the entire number of bolts 



320 A PRACTICAL TREATISE ON FOUNDATIONS. 

would have been ample, and the long screw-bolts 2\ in. diame- 
ter, and \2\ ft. long, as well as a number of the other sizes, could 
have been entirely omitted, with a saving of thousands of dol- 
lars. The writer suggested these changes to the chief engineer, 
stating the useless labor and expense involved, only to receive 
the reply that the work was to be done rigidly according to 
specifications, and that the company could pay for it. The re- 
sult was that the lowest bid was over $230,000, whereas with 
reasonable requirements the work could have been done under 
$200,000. All bids were rejected ; the company undertook the 
work. Whether changes were made or whether the cost was 
more or less is unknown. This is but a sample of the reckless 
waste of money in designing and constructing many works that 
have come under the writer's observation, and is introduced 
to show the importance of designing structures with some re- 
gard to the relative strength of the parts connected and the 
connections themselves. 

It will be noticed that in this structure there is 380 lbs. of 
iron to every 1000 ft. B. M. of timber. In the caissons of the 
Susquehanna River Bridge the average iron in bolts in each 
caisson ranged from 136 to 152 lbs. per 1000 ft. B. M., being 
probably more in proportion on the smaller caissons, as many 
straps, bolts, etc., were of the same dimensions in all cases ; 
this proved ample in sinking through both sand and gravel 
and silt, and in one caisson a sudden sinking 7 or more feet 
and landing hard on rock, crushing off the lower end of the 
verticals and careening at a considerable angle with a heavy 
load on top, did not spring a leak in the timber-work at any 
point. On the Cairo Bridge, from the data before the writer, 
the iron is 414 lbs. per 1000 ft. B. M. This evidently includes 
the shafts, pipes, etc., as the amount of iron is merely given 
as so much weight supported by the foundation-bed, and as 
both the roof of the caisson and the high cribs (34 ft.) were 
open-built, there was relatively a smaller proportion of timbers 
and a larger proportion of concrete, necessitating a larger ratio 
between the iron and timbers, though the actual quantity of 
iron in pounds was small. 



ALL-IRON PIERS. 321 

Article LI I. 

ALL-IRON PIERS. 

54. IRON piers can be constructed with either cast or 
wrought iron columns. The wrought-iron columns are com- 
posed of latticed channels ; several such columns being placed 
in slightly inclined positions, these are braced with horizontal 
channels or other form of struts, and diagonal tension members 
between them. In rivers liable to great rises, bringing large 
masses of driftwood, these piers should be incased in plate- 
iron ; this is generally open work, consisting flat strips placed 
at intervals, or large lattice strips ; this while not entirely op- 
posing the current turns aside the drift and prevents large 
masses collecting or getting tangled up in the braces. Such 
piers are light and should be strongly anchored to low masonry 
piers, the piers being built up to or a few feet above low-water, 
and in very high bridges up to or above high-water. Two 
good examples of such piers can be seen, — one across the 
Alabama River, near Montgomery, and a second in a bridge 
recently constructed across the James River, near Richmond, 
Va. There are some serious objections to such piers, unless the 
masonry is carried up above high-water, in rivers carrying 
much drift or large masses of ice, and they are not common in 
such cases. 

55. A description of an all-iron screw-pile pier bridge, con- 
structed by the writer across the Mobile River, about 16 miles 
above Mobile, Ala., will be interesting and instructive. The 
total width of the Mobile River at this point was about 1000 ft. 
This distance was divided into seven spans by six screw-pile 
piers and two brick abutments resting on ordinary piles. There 
was one draw-span 260 ft. from end to end, giving two clear 
openings of about 112 ft. each. 

It may be as well to mention that screw-piles may be of 
wood or iron, solid or hollow, varying in diameter from 6 to 12 
ins. or more, having a screw-disk at one end, similar to one 



322 A PRACTICAL TREATISE ON FOUNDATIONS. 

turn of an auger, which may be from 12 ins. to 6 ft. in diame- 
ter. They are screwed into the soil, soft rock, coral reef, etc. 
Hand or steam power can be used. For ordinary piers there 
are from 6 to 8 piles to the pier. The bearing surface being 
the sum of the areas of the screw-disk, the friction of the 
material on the surface of the shaft will add something to their 
bearing capacity. 

56. In each of the screw-pile piers in the Mobile River 
there were 8 solid wrought-iron shafts, diameter of screw-disks 
4 ft. The pivot pier was composed of one centre shaft 8 ins. 
diameter, and 10 shafts of 6 in. diameter distributed around 
the circumference of a circle about 25 ft. diameter. The screw- 
disk for the centre shaft was 6 ft. diameter. All other shafts 
were 6 in. diameter with cast-iron screw-disks 4 ft. diameter. 
The rectangular piers were formed in two rows, 4 piles to each 
row. The piles in each row were 8 ft. centres ; the rows them- 
selves were 9 ft. centres. The piles were braced by eye beam 
struts connected around the shafts b)^ collars which were 
bolted to the beams, and diagonal tension rods in both vertical 
and horizontal planes. The piles were capped with heavy 
cast-iron pieces bolted together through flanges, short wrought 
beams resting lengthwise of the pier on the caps, and on these 
a thick iron bridge-seat. All parts well bolted together. The 
eye-beam struts with the horizontal diagonal rods were called 
girt frames. Three or more of these were used according 
to the height of the pier above the bed of the river. Drawings 
and full details of these piers are shown in Plate XXI, Figs. 
1, 2, and 3. 

57. The piles of the pivot pier were braced by eye-beams 
between the piles and radiating from the centre, and a system 
of diagonal tension rods in various inclinations. These piles 
were also capped and connected together on top by large cast- 
iron pieces bolted together, upon which was placed the neces- 
sary turn table arrangements. 

The general lengths of the spans were about 142 ft. The 
design of the superstructure was the well-known but little used 
post truss, in which both the tension and strut web members 



ALL-IRON PIERS. 323 

are inclined. The original contract contemplated screwing the 
piles to a depth of 45 ft. below the bed of the river ; the actual 
result was that the greatest penetration below the bed of the 
river was i8£ ft., and the average 15^ ft. and then in one or 
more cases the shaft commenced to twist, and in all cases the 
steel teeth, presently to be explained, cut iron shavings from 
the pile, without turning or screwing them into the material, 
which was a fine compact sand. 

These indications were accepted as satisfactory proof that 
sufficient bearing power had been secured. One idea in adopt- 
ing this kind of pier was to prevent scouring by offering as 
little obstruction as practicable to the current, and thereby 
prevent any scouring. These piers are light but strong and 
stiff, and have now been in use over twenty years, and carry 
safely the heavy rolling loads of the present day. 

58. Some little detail concerning the manner of sinking 
them will be given. The depth of water varied from 10 to 20 
feet; the height of pier above water, about 9 feet. At the 
site of the bridge the rise from floods was only a few feet ; the 
immense volumes of water from the rivers above dividing 
among many bayous, and spreading over the entire swamp. 

The shafts were rolled in sections of different lengths ; the 
bottom section, which was connected with the screw-disks by 
four steel pins, was about 22 feet long. This, when set in place, 
would reach above the water; on top of this a heavy cast-iron 
sleeve about 3 feet long, fitting snugly around the pile, and fast- 
ened to it by two steel pins at right angles. Another section 
12 or 15 feet long was then lowered into the sleeve, and resting 
on the top of the first shaft. Steel pins were then passed 
through sleeve and shaft. The machine for turning the piles 
consisted of a rectangular base frame of timber, to the corners 
of which were fastened four stout pieces of timber meeting 
at a point above, which was slightly out of centre in one 
direction, so that the shaft when standing vertical and in 
position would clear the timbers of the frame. About four 
feet from the bottom of the" frame a large cog-wheel, sup- 
ported horizontally, was placed ; the spokes of this whcsl 



324 A PRACTICAL TREATISE ON FOUNDATIONS. 

rested in an iron collar about 15 ins. diameter, carrying on 
the inside two friction-rollers. The shaft passed through 
the centre of the collar. A strong jacket with flanges in 
two halves, and carrying on the interior several solid steel 
plugs with sharp teeth, was adjusted to the shaft and drawn 
by bolts close to it, indenting the teeth into it by bolts 
through the jacket-flanges, the lower ends of which rested 
against the friction-rollers ; a worm-screw with ordinary crank- 
arms could be thrown in or out of gear with the cog-wheel. A 
number of men turning the worm by its arms imparted a circular 
motion to the cog-wheel, which turned the jacket and the em- 
braced shaft, thereby screwing the disks into the bed of the 
river. This could be continued until the top of the jacket 
reached the rollers ; the jacket was then loosened and lifted to 
a distance equal to its length, again tightened to the shaft, 
when the power could again be applied. From 8 to 10 men 
could apply power enough to twist the shaft. The use of 
steam might have been more economical and rapid, but would 
not have been more efficient. The greatest difficulty existed 
in starting and holding each pile vertical and in its exact posi- 
tion ; this was essential, as otherwise the caps and girt-frames 
could not have been adjusted to the piles, as all parts were 
made in Chicago and shipped to the bridge-site. The work 
was carefully and conscientiously executed by Gen. Win. Sooy 
Smith. In addition, every pile had to be brought to exactly 
the same level on top, as it would have been very troublesome 
and expensive to cut them to a level. This was accomplished 
in the case of every pile, except the large centre-pile of the 
pivot pier, which could only be screwed 9 feet into the sand ; 
this was clipped off with the cold-chisel. The greatest error in 
the levels of the top did not exceed one eight of an inch. 

When from any cause it is necessary to reach greater 
depths than the piles can screwed by turning, the limit of 
which is reached when the piles show signs of twisting, or the 
teeth or other hold upon the pile is insufficient, resort can be 
had to the water-jet. This method has been used successfully. 
It is stated, no doubt, upon reliable authority that the use of 



LOCATION OF PIERS. $2$ 

the jet is more effective when applied to the upper surface of 
the screw-disc, rather than, as would seem natural, to the under 
side and the point of the pile. Why so, does not seem entirely 
clear. Applied to both under and upper surfaces would, no 
doubt, be advantageous. In this process there would seem to be 
no cause of trouble when the screw-disc was not over from 12 to 
18 inches in diameter; but with discs from 3 to 6 feet in diam- 
eter it would be troublesome to hold a pile exactly vertical and 
in exact position, if this should be absolutely necessary, as in 
the case already mentioned. On this point the writer, how- 
ever, cannot express an opinion, as he has no experience in this 
method of sinking screw-piles. Each pile in each pier had to 
be located separately from an established base on the shore 
or from completed piers, as no staging could have been con- 
structed steady enough to maintain any centre point. 



Article LIII. 

LOCATION OF PIERS. 

59. There are many methods of locating the piers of large 
bridges across rivers. They all, however, resolve themselves 
into the method of triangulation, or direct measurement from 
some established base on the shore ; and as it all depends then 
on the base-line, this should be accurately measured, and its 
direction and location in regard to the centre-line of the bridge 
should be carefully selected. It should be as nearly at right 
angles to the centre-line as practicable ; and its length should 
be equal, or nearly equal, to the entire width of the river, so 
that distances from the end of the base, equal to that of each 
pier from the same point, can be laid out on the base-line. It 
is, however, rare that both of these conditions can be realized 
in practice ; especially as it is also desirable that the base-line 
should be laid out on ground as nearly level as practicable. This, 
however, is not a matter of so much importance, as with due 
care perfectly accurate distances can be measured on rolling 
or rough ground. But it is essential that each pier shall be 




326 A PRACTICAL TREATISE ON FOUNDATIONS. 

easily visible from its own triangulation points, and that the 
entire hase shall be seen from either end. The best adjustment 
of the base to all of these conditions must be made. No angle 
in a triangle should be less than 30 degrees, nor greater than 
120 degrees. The base may be somewhat less in length than 
the width of the river. It is advisable to have a base 
on both sides of the river, the one used as a check 
on the other; 2d. If points can be found, two on 
each side of the river, so that the lines joining two 
of them is near to, and approximately parallel to, 
the centre-line of the bridge, and so situated that 
each and every pier can be seen from both extremi- 
ties of each line, these lines form an excellent basis, 
and are good checks on each other. The lengths 
of these lines have to be determined from bases, 
which form well-conditioned triangles with them ; 
but otherwise selected without reference to the centre-line 
of the bridge or the positions of the piers. If the two sec- 
ondary bases across the river are in sight of each other the one 
can be used to calculate the length of the other, thus insuring 
the accuracy of both. These lines should be far enough from 
the centre-line so that the directions of each pier from its ex- 
tremities shall form well-conditioned triangles with the base ; 
3d. Or bases can be measured on opposite sides of the river, 
extending in opposite directions — one up and one down stream. 
Upon these lines points can be established, so that the lines 
joining two of the points shall intersect the centre-line at the 
centre of each pier. This method has the advantage that when 
these points are once accurately located it is not necessary to 
turn any angles to locate the position of a pier, as it depends 
upon the intersection of two lines ranged by foresights, and the 
further advantage that the engineers are working from largers 
to smallers, and any error in centring the rods with the tran- 
sits are divided or lessened, eliminating two sources of error : 
that of working from smallers to largers, if the one base is too 
short, and the error of graduation in the limb of the transit, as 
well as the error in reading the vernier. In addition, this 



LOCATION OF PIERS. 



327 



method only requires the measurement of one angle for each 
base, viz., the angle between the base-lines and the centre-line 
of the bridge ; the base-lines need not be parallel. The dis- 
tances from ends of the base-line to each pier, measured on the 
centre-line, must be known. Having determined the width of 
the river between points established on the shore on the centre- 
line, and the position of the piers on this line, the piers can be 
located by either of the three methods. Figs. 9, 10, and 1 1 show 

Fi g- 9- Fig. 10. 




Fig. 11. 
Methods of Locating Position of Piers from Base-lines. 

these methods in their order as above described — in which AB 
is the centre-line ; BC, the base-lines, from which the piers are to 
be located ; 1, 2, 3, 4, and 5, the positions of the piers. The 
base-lines in Figs. 9 and 10 are shown as passing through the 
centres of the shore piers, and the triangulation points at the 
centres of the piers on the other side of the river. These may 
occupy any position with respect to the piers that may be 
found most convenient. In Fig. 9 the angle at B is known, and 
also the distances BG, BH, BK, and B2, B3, B4, and B$, and the 



328 A PRACTICAL TREATISE ON FOUNDATIONS. 

angles at G, H, and K calculated. In Fig. II the bases B. 2 C 
B 1 C 1 are calculated from the measured bases B lf D x , and DC 
respectively, the accuracy of which can be tested by calculating 
B C from B„C used as a base. The distance from i and 5 
piers can then be calculated from either BJC or B X C X as a base 
— these piers being located on the banks of the stream, as may 
be determined by purely practical considerations ; the main 
object being to place them far enough back from the sloping 
banks to preclude any danger from caving in of the banks. 
The angles BfiC and C2B 2 are then easily calculated in the tri- 
angle \B. 2 2, AB„, 1.2, and the angle B.A.2 are known, from which 
ii>,2 can be calculated; then2i? a C?= l.B^C— l,2? s 2, and similarly 
for all other required angles. As seen DC and B X D X can be meas- 
ured where convenient without reference to the centre-line AB. 
In Fig. 10, having measured the base BC, lay off the distances 
B K, BH, BG, and BC, approximately equal to B4, B$, B2, and 
Bi, respectively. The proper distances AG 1 , AH^, and AK l 
can be easily calculated. For instance, we know in the triangle 
B2G, BG, B2, and the angle GB2, then angle G2B can be 
calculated. Then in the triangle A2G l we know the angle A2G v 
= G2B, the angle 2 A G 1 , and the distance A2, from which cal- 
culate AG V In every case two transits are required to locate 
the position of the piers ; one of them at least should be of first- 
class make, with a good telescope and accurate limb gradua- 
tions. Several points in the prolongation of AB on each side 
of the river should be established ; and large hubs of good solid 
wood, from 2^ to 3 feet long, should mark these points — the 
exact point marked by a tack. The top of these hubs should 
be even with the surface of the ground, or better, a few inches 
below, to prevent its being disturbed by hauling over or near it. 
The centre-line should be well and distinctly marked on the 
faces of the piers before they rise above the line of site. The 
intersection of all the oblique lines, with the faces of piers, 
should be marked also. A line of red or black paint answers 
for this purpose ; and on the completion of the pier its exact 
centre, both as to distance and line, should be marked by two 
chisel-scratches intersecting and painted, or by drilling a small 



LOCATION OF PIERS. 320 

hole and inserting a short iron rod. In measuring the base-lines 
large hubs should be driven not over 12 to 15 feet apart, accu- 
rately lined, on level ground ; these should then be sawed off 
square to the same level. On rolling ground as many should be 
cut off to the same level as practicable ; and any change in the 
level required is to be made at one point, and then cut off as 
many as practicable at the new level. The base can then be 
measured with an accurate steel tape ; driving tacks in line, and 
at the proper distances apart, to mark the important points. 
The most satisfactory method is to have made at least three 
timber base-bars, 12 to 15 feet long; these are made of two 
pieces of white pine about 1^ in. thick and 3 in. wide; the one 
set edgewise on, and at right angles to, the other, and bolted 
together, showing a T-section. These can be lightened by 
rounding gently from the centre to the ends. Brass strips with 
pyramidal-shaped ends are then bolted to their ends. Having 
obtained a 3-ft. standard U. S. steel bar, these bars are accu- 
rately measured by them, the brass point being filed to some 
exact distance, say 15 feet — the brass point not being over 1 in. 
square ; the measurement being made at the standard tempera- 
ture as nearly as practicable ; the sketch (see Fig. 8) shows one 
end of the base-bar ready for use. These three bars should then 
be placed in line, resting on top of the hubs, with their brass 
points in contact ; the rear one should then be moved to the 
front and placed in contact with the front one, and so on ; the 
extreme front end being marked on the tack with a scratch 
to avoid slight errors caused by moving the rods. This should 
be continued from end to end of base, and repeated several 
times; then checked by steel tape-measure. In a number 
of bridges across wide rivers, with high piers placed at all 
intervals from 100 to 525 feet apart, the writer has never 
had any appreciable errors in locating the piers. 

60. He has, however, relied to a great extent on measure- 
ments with steel wire, using generally what is known as No. 
10 pianoforte wire. This is very strong and light, can be 
pulled almost to a horizontal line with a spring-balance ; a pull 
of 15 to 20 lbs. is sufficient. The base-line was measured 



330 A PRACTICAL TREATISE ON FOUNDATIONS. 

carefully, as already described ; after which all hubs, except 
those marking the lengths of the span, should be removed, so 
that in stretching the wire it will have the same sag that 
it would have when locating the piers. These hubs were well 
protected, so that they could not be disturbed. A tarred 
string will adhere to the wire when tightly wrapped around 
over a distance of I to i^- ins., the inner edges of the string 
being at the required distance apart from tack to tack on the 
base-line. This distance being measured with wooden rods of 
standard lengths, is independent of the temperature. The wire 
should be stretched on the base before measuring the span. The 
contraction or expansion can be allowed for on the spring, 
when appreciable, without moving the strings ; and after 
measuring the span it should again be tested on the base. 
This is a safe precaution, but the tarred string never slipped 
in the writer's experience. A change of temperature of 180 
would change the length of a wire 525 ft. long 0.66 of a foot, 
— about 8 inches, coefficient of expansion taken at .00125. 
Assuming that the strings were adjusted at a temperature of 
6o°, then at a temperature of 90 ° the length would be al- 
tered 1^ ins., that is, lengthened ; and at 30 it would be 
shortened 1^ ins. These would be nearly the extreme ranges 
of temperature. But this is of no moment, as the wire is 
tested on the base before measuring. A little greater or less 
pull on the spring-balance would correct the error. Both the 
transit and wire should be used to check each other. The 
transit-rod for this work should be a f or \ in. pipe, brought to 
a well-defined point at one end, and painted in alternate 
lengths of a foot red and white. 

LOCATION OF BRIDGES. 

61. The writer has been often asked what are the consid- 
erations determining the location of bridges. The factors enter- 
ing into this matter are various. 1st. Economy; this involving 
such questions as the width of the river, the depth of the water, 
the nature of the material forming the bed of the river, the depth 
of the foundation-bed below the surface, etc.; the slowness or 



LOCATION- OF BRIDGES. 33 1 

rapidity of the current. These questions must all be consid- 
ered and that site selected which costs the least, if economy 
alone is to be considered. High banks on one or both sides 
are generally desired, as they decrease the cost of the ap- 
proaches, though they may increase the cost of the bridge 
proper. Again, without regard to cost of the bridge proper, 
the necessary or best location of the line on either side of the 
bridge may be the controlling consideration. This may or may 
not be controlled by a question of total cost. A good illus- 
tration of this is in the case of the Susquehanna River bridge 
at Havre de Grace. If the line had been located two miles 
higher up the river, a bridge could have been constructed rest- 
ing on solid rock exposed at low-water, instead of building a 
bridge at a point where we had to go to a depth of 90 ft. 
below water surface for a foundation-bed. This would have, 
however, lengthened the line some four or six miles, and would 
have caused some short curves. Six miles extra distance 
causes much extra cost, both in construction and in mainte- 
nance for all time, and means ten or fifteen minutes' more 
time in running between Baltimore and Philadelphia. 

62. Bridges should be easily approached from both direc- 
tions, avoiding both sharp curves and steep grades. In fact, 
we are often forced to build at certain points, no choice being 
left to the engineers, especially in crossing navigable rivers, as 
permission has to be obtained from the Secretary of War, and, 
in addition, he determines the lengths of the spans, heights of 
the piers, as well as site of bridge. The necessities of the case 
first determine the site. After this economy, considered as ap- 
plied both to the bridge and the construction of the line on 
both sides, determines the selection of a bridge site. 

63. Economy also demands the height of the piers to be 
as little above high-water as practicable. On navigable 
streams this height is regulated ordinarily by law, whether a 
draw-span is used or not. Likewise, to a large extent, the 
position of piers, as well as length of span, is determined by 
law. But when not so regulated, it may be stated as a gen- 
eral rule that, where the foundations are inexpensive, rela- 



33 2 A PRACTICAL TREATISE ON FOUNDATIONS. 

tively speaking, a number of piers and short spans will be 
economical. Where the foundations are deep and costly, few 
piers and long spans are to be preferred. In either case the 
aim should be to make the total cost as small as possible by 
many trials with different lengths of span. 

64. It is advisable, as far as possible, to avoid bends in the 
river, as the piers should always be placed with their longer 
axis parallel to the current ; for the same reason, the line 
should cross the stream at right angles to the direction of the 
current. 

65. The following table gives a few examples of the longest 
bridges, longest single spans, with the highest piers and lowest 
foundation-beds now in existence: 

Total Longest Nature of , Depth Sunk » 

Length. Span. Foundation. Low-water. High-water. 

New York Suspension Bridge 5890 1595 Caisson 78 

Poughkeepsie Cantilever 4595 54S Crib 132 

Havre de Grace Truss 6300 525 Caisson 90 94 

Memphis Cantilever ,. 7997 790 " 96 131 

Hawkesbury Truss 416 Crib 153 160 

The Forth Cantilever, 2 spans, 

each 1710 

St. Louis Steel Arch 1550 520 Caisson 94 136 

The above data are taken, in some cases, from unofficial 
sources, but are very close approximations, and serve the pur- 
pose of showing the depths which can be reached by well- 
known methods of construction. 



Article LIV. 
THE POETSCH FREEZING PROCESS. 

66. The writer will give a short description of the freezing 
process, which has been used to a limited extent in sinking 
very deep shafts, and generally through the most difficult and 
treacherous material with which the engineer has to deal, 
namely, quicksand, which always is troublesome and expen- 
sive to encounter, and often has opposed an insurmountable 
barrier to further progress. It has been used in Europe to a 
considerable extent, but to a very limited extent in this coun- 



THE POETSCH FREEZING PROCESS. 333 

try. It has been successful where applied, but the public are 
as yet to a great extent left in ignorance of its relative cost, 
nor has its possibilities been sufficiently developed to form a 
definite opinion as to its range of applicability. The owners 
of this patent are the well-known and reliable firm of Sooy- 
smith & Co., and it will doubtless be pressed to its full practi- 
cable value and usefulness by them. The following brief de- 
scription is obtained from them and other sources : 

67. A series of vertical pipes 10 ins. in diameter, open at 
both ends, are sunk around the space to be excavated to rock 
or some impervious strata. These may be called the pilot 
pipes. Inside of these, pipes 8 ins. diameter, tightly closed at 
the lower ends. Inside of these latter pipes, smaller pipes, 
open at the bottom, are inserted. Each set of pipes, being 
connected in a series by itself, communicate either directly or 
indirectly with a cooling tank. The freezing liquid is pumped 
through the inner small pipes and returns through the outer 
larger pipes to the cooling tank, to be cooled again and again 
circulated through the pipes. For convenience and economy 
these pipes are arranged in a circular form around the space to 
be excavated. As the cooling mixture circulates it freezes the 
soil in the form of an increasing solid cylinder or core, which 
unites at points between the pipes, thus forming a solid frozen 
wall around the space, the enclosed space being either entirely 
or partly frozen. The excavation is then commenced, leaving 
sufficient thickness of frozen wall to resist the outside pressure. 
For safety, however, in the present development of the process 
the shafts are, or have been, lined with frames and sheeting as 
the excavation progressed. The costs then are : first, the cost 
of the necessary machinery and plants, including pipes and the 
freezing fluids, etc. ; second, the sinking of the pipes to the 
required depths, and subsequent removal of the same ; third, 
the excavation of the material in its frozen state. This last 
must necessarily be very expensive, as it is estimated that the 
crushing resistance of frozen quicksand may be as high as 1000 
lbs. per square inch. Lining may not be necessary when the 
frozen wall is cylindrical, with small diameters ; but with large 



334 A PRACTICAL TREATISE ON FOUNDATIONS. 

rectangular piers they would have to be of very great thickness 
to resist the outside pressure, unless well braced against it. 
Experience will, however, settle these points, and speculation 
is of but little profit. Such is the process, and very simple 
it is. 

68. The conductivity of earthy materials either partly or 
fully saturated with water is not known, and as there is doubt- 
less more or less movement of the water in the water-bearing 
strata, a sufficient degree of cold must be provided and kept 
up during the entire time of excavating and lining the shaft. 

It is estimated that, as the specific heat of quicksand is 
only one fifth as much as that of water, the amount of cold 
necessary to freeze i cu. yd. of water would freeze 2|- cu. yd. 
of quicksand, and that one horse-power per day would freeze 
362 lbs. of water. 

69. Ordinary refrigerating machines act upon the principle 
that when a gas is compressed its temperature rises and when 
it expands its temperature falls. Ammonia, having a high 
specific heat, is probably the most economical gas to use. 
" The ammonia may be compressed mechanically, or it may be 
compressed by the tension of its own vapor heated in a still," 
which is cooled by passing through coils of pipe immersed in 
water, retaining its pressure in the still, and when allowed to 
expand in other coils or pipes its temperature falls rapidly to 
well below zero. In this condition it absorbs heat from any- 
material with which it comes in contact, by which its own tem- 
perature rises. It is then cooled, allowed again to expand, 
with the ultimate result of freezing the earth or water sur- 
rounding the pipes. The efficiency of the now existing ma- 
chinery is only about twenty-five per cent of the energy 
applied. The cold gas may be circulated directly through the 
pipes in contact with the soil, or it may more conveniently be 
employed to cool a brine, which is then circulated through the 
pipes. At Iron Mountain, Mich., where a shaft 15 ft. square was 
sunk to the depth of 100 ft., there were used twenty-seven pipes 
8 ins. diameter, arranged on a circumference of 29 ft. in diameter, 
the pipes being a little over 3 ft. apart. In ten days from start- 



THE POETSCH FREEZING PROCESS. 



335 




Shaft rank at Iran Mountain, Mich. 

PCETSCH-SOOYSMITH FREEZING CO 

Ha. 2 Nauaan Street. New York. 
Fig. 12. 



336 A PRACTICAL TREATISE ON FOUNDATIONS. 

ing the frozen cylinders were in contact. From this time the 
enclosed space froze more rapidly than outside the pipes, for 
obvious reasons. Strata containing little water were frozen to 
a greater distance from the pipes than those containing much 
water. " An ammonia machine of the compression type (the 
ammonia compressed mechanically) was used. Its capacity 
was twenty-five tons of ice, or fifty tons refrigerating capacity, 
per day. The wall was frozen and the excavation to the ledge 
of rock (ioo ft. down) was completed in two and a half months 
from the time that the ice machine first started." The cir- 
culating brine was calcium chloride, on account of its low 
freezing-point, high specific heat, and non-corroding action on 
iron pipes. " The best results are obtained from such a rate 
of circulation that there is but little difference in temperature 
between the outgoing and incoming brine. A very efficient 
temperature for the outgoing brine is io° F. below zero, and 
pumped at such a rate that the return flow is 2° higher." The 
subject is a very interesting one, and it remains as yet to be 
determined, the cost as compared with other methods at the 
same depth, its certainty as against leaks, breaking in of walls 
at great depths, the relative time taken to complete structures 
requiring such large bases as the piers of bridges; and, until 
applied on such large scales which may develop either unknown 
difficulties or advantages in the process, it would be unjust to 
the owners and to the engineering profession alike to forebode 
either evil or good concerning it, and it is to be hoped that its 
owners may be bold enough to make the experiment on a large 
scale. The drawing, Fig. 12, page 335, shows positions and 
arrangement of pipes, the excavation made through sand, 
gravel and bowlders to rock, and the timber lining for shaft. 

Article LV. 

QUICKSAND. 

70. HAVING now described the various materials on which 
structures are more usually built, and the many means adopted 
to secure a safe bearing for both shallow and deep foundations, 
a few facts in connection with the nature of, and difficulties 



QUICKSAND. 337 

to be encountered in dealing with, the most troublesome, 
treacherous, and almost unmanageable material, namely, 
quicksand, will be interesting and instructive. 

It is not uncommon to consider as quicksand any kind of 
material, so saturated with water, that it will flow more or less 
freely when its natural condition of equilibrium is destroyed, by 
excavating pits, trenches, shafts, or tunnels. This material may 
be found on the surface underlaid by a firm material, or it may 
be found in strata of greater or less thicknesses confined by firm 
strata both above and below. When on the surface, though 
presenting some difficulties, it can be dealt with by any of the 
methods heretofore described, and will not therefore be further 
discussed here. The most troublesome case arises when strata 
of quicksand are met with at considerable depths below the 
surface. The reasons are many and evident : the pressure is 
likely to be much greater ; the flow of the material allows the 
superincumbent strata to settle, bringing an almost irresistible 
pressure upon the sides of the structure, either crushing it in 
or at any rate throwing it out of line, increasing greatly the 
amount of material to be excavated ; these causes adding 
enormously to the cost of the structure and time required to 
complete it. Sometimes the crude methods of overcoming these 
difficulties, regardless of delay and cost, such as the free use of 
straw, brush, shavings, extra sheeting and bracing, have proved 
successful, but often, after repeated efforts, and expenditure of 
money, the further prosecution of the work had to be aban- 
doned. The discovery and application of the freezing process 
was a source of hope and encouragement, and that it is effec- 
tive cannot now be questioned or denied. This and the intro- 
duction of a new method, presently to be explained, requires a 
more accurate understanding and definition of the loose ma- 
terial called quicksand. 

71. In a pamphlet written by Mr. E. L. Abbott, dated 
Nov. 20, 1889, on the freezing process, and doubtless having; 
the sanction of such high authority as the Sooysmith Com- 
pany, quicksand is defined as any earth which " will in some 



338 A PRACTICAL TREATISE ON FOUNDATIONS. 

degree run like a fluid when mixed with water." He, however, 

o 

states that any kind of sand mixed with a small amount of 
clay possesses this property, but that the most troublesome 
material contains but a small per cent of very fine sand. " This 
material when undisturbed may have some consistency " (italics 
mine) ; when disturbed will flow through any minute opening. 
In the Engineering News, April 28, 1892, in which the new in- 
vention of Mr. R. L. Harris is described, is found this state- 
ment : " This quicksand, when dry, is an impalpable powder. 
When saturated with water it is very compact and hard until 
disturbed. Under the pressure of a slight depth it becomes 
apparently almost solid ; hammer strokes of 300 ft.-lbs. aided 
by a wash pipe, causing 2-in. iron pipes to penetrate upon an 
average less than o. 1 in. per blow. Upon being agitated with 
water the quicksand becomes alive and runs like mush. Its 
currents under pressure move glacier-like, and are seemingly 
irresistible." 

The writer built some culverts on a quicksand ; the solid 
material composing it was an impalpable powder, and it would 
run into the excavation like " mush." He also drove piles for 
a trestle several hundred feet in length through what was 
called quicksand. No difficulty occurred so far as penetration 
was concerned, the piles moving several feet at a blow, but 
immediately after impact the piles would lift the hammer, and 
removing it, they would spring up suddenly to the height of 
several feet. There is clearly several kinds of this troublesome 
material. 

72. The freezing process is applicable whether the solid 
material composing the quicksand is clay, sand, or mixed clay 
and sand. Time and expense alone are questions to be con- 
sidered. This method has been explained. 

73. The latest method (see Engineering News) is novel; ex- 
periment proves it effective in the material described. The 
importance of knowing the nature of the solid material arises 
from the method adopted, as it depends upon the hardening 
of injected cement. It is generally accepted that pure cement 



QUICKSAND. 339 

mixed with clay or mud or exceedingly fine sand * either does 
not harden at all, or at any rate imperfectly ; and in such cases 
the cement must be " doctored " with sand, plaster of Paris, or 
anything else that will solidify under the existing conditions. 
In the case to be described, the work consisted in thus solidify- 
ing a trench for a large intercepting sewer, the laying of which 
had baffled all the efforts of the engineers, and practically 
bankrupted the contractors. 

When such high authority as the Engineering News pub- 
lishes the following : " This [the freezing] process has proved 
very useful in many cases, but from its very nature it requires 
a somewhat expensive refrigerating plant, a long-continued 
circulation of the freezing fluid, and a continuance of the cir- 
culation so long as it is desired to keep the material solid, if it 
is to be exposed for any considerable time." 

" The method to be described is the invention of Mr. 
Robert L. Harris, N. Y. Am. Soc. C.E., and it has been re- 
cently tested experimentally on a sufficiently large scale to 
establish fully its practicability, under proper conditions, in our 
judgment. It seems likely to prove a competitor of the 
freezing process in some fields, besides having useful applica- 
tion in cases where that process would not be suitable." 

The writer needs no excuse for giving a detailed descrip- 
tion of the method. 

The principle involved is simple, and depends only upon the 
fluidity of the material when mixed with water. If two pipes 
be sunk into the material at distances apart varying with the 
depth, and a current of water be forced through one of them, 
it will seek an outward passage along the line of least resistance, 
and will issue, carrying some of the material from the other pipe 
along with it, washing a channel between the two pipes, and 

* The writer condemned a large quantity of exceedingly fine sand; subse- 
quent tests and experiments satisfied him that the mortar produced was equal 
to any previously used on the same work with a good-sized and sharp-grain pit- 
sand. Two large piers were built of this fine sand which stood immersions in 
flood water, covering it shortly after being mixed and used (the same day), it 
also stood well a severe winter on exposed surfaces of masonry. It was an 
almost impalpable powder when dry. 



340 A PRACTICAL TREATISE ON FOUNDATIONS. 

by using a number of pipes a chamber will be scoured out. 
Channels or chambers being made, " the plan was then to sub- 
stitute for the channel-making stream of water " some cement- 
ing material in a fluid condition, and by proper arrangement of 
valves shut the outlet pipes as the cementing fluid reached 
them, and by applying pressure not only make the cementing 
fluid fill the chamber, but also permeate the adjacent materials, 
thereby forming a floor between the pipes and by gradually raising 
the pipes additional layers would be formed uniting into a solid 
wall. The trench for the sewer was 12 to 16 ft. wide and from 
20 to 30 ft. deep in quicksand ; the length through this material 
was over 4000 ft. An attempt to pump out this material was 
made, and an area of forest about 150 X 75 ft- settled several 
feet, inclining large trees at a considerable angle and doing 
other damage. He found that quicksand in solution took 
hours to settle, but on introducing the cementing material all 
solid matter settled rapidly, leaving clear water on top ; hence, 
by agitating the material, a large quantity would be placed 
in suspension, and the introduction of the cementing ma- 
terial would result in an intimate mixture and precipitation of 
the material, ultimately forming a solid floor. Pipes had been 
lowered to a depth of 25 ft. and at distances of 4, 10, and 14 ft. 
apart, which established fully the circulating theory. Then 4 
pipes were sunk at the angles of a quadrilateral 4 ft. on the 
side, and sunk 17 ft. below the excavated surface. A chamber 
vas formed, and after maintaining the cavity for three days, 
the cementing material was forced through the pipes into the 
chamber, resulting in a fairly solid and complete floor. Two- 
inch pipes were first sunk, and a small cavity hollowed out at 
he bottom. Smaller pipes, carrying suitable valves at the 
bottom for closing the pipes against upward currents, were 
lowered through the larger ones. When the ends of the smaller 
pipes were below those of the larger, the circulation was 
unobstructed ; by slightly raising the smaller pipe, the fluid 
could not escape. The blocks of cemented quicksand were 
from 3 to 6 ins. thick, reaching from pipe to pipe; they were 
hard and solid, and homogeneously solid — in some cases for a 



QUICKSAND. 



341 



thickness of 6 ins. or more. The following figures illustrate 
the process: Fig. 13 shows the manner of making a solid wall 
by successive slight lifts of alternate pipes, using first one and 
then the other for the downward current, and the two adja- 
cent pipes for the upward current. In forming a floor (see 
Fig. 14), the pipes are simply distributed over the space at 
regular intervals, and sunk practically to the same depth ; the 
shaded portions representing the solid layers or blocks of 








PLAN. 









O 










O 


O 







O 












■mi 



FlG - T 3- Fig 14. 

Cementing, through Pipes, Quicksand for Foundations or Walls. 

cemented quicksand. Great claims are made for this process 
in protecting shores, driving shafts, and tunnels, and in putting 
in foundations forming the base of the materials in place. 

The essential principles are to so arrange the pipes as to 
allow free circulation while washing out, and to close the dis- 
charge pipes when the cementing material is forced in. Pipes 
should not be allowed to be caught in the hardened material. 
Whatever may be the possibilities of the method, which must 
be established on a sufficiently large scale by experiment, the 
process is simple, and seems to be effective. Outside of the 
pipes the only plant required is a pump of sufficient capacity 



34 2 A PRACTICAL TREATISE ON FOUNDATIONS. 

to produce a good current in a 2-inch pipe, and a moderate 
pressure when introducing the cementing material. 
Both of these methods are patented. 

74. In case of the culverts founded on quicksand, the writer 
simply spread the base by logs crossing each other in several 
course, and covered with plank upon which the masonry rested. 
Although this method is not to be recommended, and should 
not be used at all under very heavy structures, the culverts have, 
nevertheless, carried safely railway trains for years. Particular 
care was taken to sheet around the sides and ends so as to 
confine the quicksand as much as practicable. 

75. Hollow brick or concrete or iron cylinders and timber- 
lined shafts are often sunk to great depths through these soft 
materials, and ultimately filled with concrete or masonry col- 
umns or pillars. The sinking is effected by simply excavating 
the material from the inside and adding weights, if necessary, to 
the cylinders sufficient to make them sink against the friction ; 
or by the ordinary method of suspending the upper top setting 
or frame at the surface, and as the excavation advances plac- 
ing other strong frames of timber at intervals of 4 or 5 feet, 
and inserting plank sheeting on the outside resting against the 
frames ; or in softer materials, after setting a frame, the sheet- 
hie is driven around it on the outside, and driven ahead so as 
to keep in advance of the excavation. When the sheeting 
shows signs of springing or bending another frame is inserted 
and another set of sheeting started between the last frame and 
the sheeting from above. With brick or concrete cylinders 
the bottom must rest on a timber or iron curb, consisting of a 
short cylinder of timber or iron framed with a cutting edge, 
and on top a ring of timber or iron of sufficient width to carry 
the masonry, and supported by brackets fastened to the sides 
of the curb. Though often used for foundations, such methods 
are more generally applicable to sinking shafts in mining opera- 
tions, or in connection with driving tunnels, and constructing 
piers for bridges. Iron cylinders were- used in founding the 
City Hall of Kansas City, mentioned in another page. Hollow 
brick, concrete and iron cylinders for piers of bridges will be 
described later. 



FOUNDATIONS FOR HIGH BUILDINGS. 343 

Article LVI. 

FOUNDATIONS FOR HIGH BUILDINGS. 

76. In the last few years the construction of high buildings 
in cities has rendered necessary a more careful and thorough 
examination into the bearing power of soils and remodelling 
the underground columns and supports, so as to secure safe 
bearing areas and at the same time so reduce their cross-sec- 
tions that they may occupy as little space in the underground 
compartments as practicable ; and perhaps more thought has 
been given to this subject and greater developments in this di- 
rection have been made in the city of Chicago than anywhere 
else. Until very recently it has been supposed that the clay 
was underlaid by a thick layer of quicksand or some soft ma- 
terial. The practice has been to guard carefully against cut- 
ting through this clay, and as the height of the buildings has 
been increased the base of the walls and column supports has 
been gradually spread and enlarged, so as to maintain a unit 
pressure not exceeding from 3000 to 3500 lbs. per square foot. 
Under some structures piles have been driven, as it was feared 
that the limit of safety had been reached for sufficient support 
by direct bearing. This has not been considered in some 
cases as entirely satisfactory or even as an improvement 
over the former method, unless the piles are made long enough 
to reach to the bed-rock, which is from 50 to 60 ft. below 
the surface, and are driven at the bottom of excavations 15 
or more feet deep, so as to insure that all wood-work, piles, 
caps, and flooring, when used, should be certainly below the 
line of constant moisture. It is claimed that careless driving 
was the cause of the inefficiency of the piling. Following 
upon this, Gen. William Sooysmith read a paper arguing that 
some method of reaching the rock should be adopted, and 
pillars of stone with polished beds, so as to do away with mor- 
tar, should be used to bring the foundation up to or near the 
surface of the ground, claiming that such a pillar would be four 



344 A PRACTICAL TREATISE ON FOUNDATIONS. 

times as strong as one of ordinary masonry. These methods 
were argued against as being entirely useless and unnecessarily 
expensive, and the claim is set forth that Chicago is underlaid 
by a solid bed of compact clay from the surface to or near the 
rock, passing into compact gravel immediately above the rock, 
and that the borings thus far made have been deceptive on ac- 
count of the water which, though existing in small quantities 
in the clay, collects in the pits and leaves the impression that 
the underlying soil is either quicksand or mud. It seems to 
the writer borings conducted as explained in the second part 
of this volume would settle this matter definitely and satisfac- 
torily, as the material can be brought up just as it exists from 
any depth, if it is silt or clay. It is admitted that proper, effi- 
cient, and systematic borings have not been made.* By these 
parties it is claimed that by the use of the combined steel and 
concrete beds a sufficient spread of base can be obtained to bear 
safely any height of building likely to be required. And so this 
matter stands, ably argued on both sides, but, as it seems to the 
writer, without sufficient and reliable data being determined 
to settle the question. It will be of interest, however, to see 
what has thus been accomplished. The economizing in the 
question of cellar spaces is well illustrated in Figs. 15 and 16. 
Fig. 1 5 shows a masonry pier resting on a concrete base ; Fig. 16 
shows a steel rail and concrete footing resting on an equal mass 
of concrete, therefore having the same ultimate bearing capacity. 
The masonry above the concrete is 7 ft. high (see Fig. 15); in 
Fig. 16 the height is only 2 ft. 6^ ins., the upper course being 
15-in. eye-beams. A similar construction, using rails for the 
upper courses and transmitting the same weight, would be only 
1 ft. 8 ins. high above the concrete. In this case the weight of 
the masonry base is 216,000 lbs. ; the weight of the steel base, 
103,000 lbs. The weight on this foundation is about 800,000 lbs., 
the weights of the foundations being respectively 20 and 13 per 
cent of the total. The saving in weight of the iron and concrete 

* Since writing the above Mr. A. Gottlieb has made a large number of bor- 
ings; about the average results will be found in the supplement to this volume. 
A full report was published in the Engineering News. 



FOUNDATIONS FOR HIGH BUILDINGS. 



345 



foundations is enough to allow an additional story. There is also 
a saving in time. The cost of constructing the stone foundation 
is a little less than the steel, but the increase of rental space 
more than compensates for this. The steel beams also enable 
the load to be distributed over a part of the area between two 








Fig. 16.— Iron Rails and Beams on Concrete Base. 



columns by beams extending from the one to the other, thereby 
bringing into bearing a part of the foundation that could not 
be utilized for this purpose in masonry columns. The concrete 
used is of the best Portland cement and broken stone — I part 
cement, 2 sand, and 4 stone. The steel rails are 75 lbs. per 
yard. When beams are used, the 10, 12, 15, or 20 in. beams 
are best. The following calculation applies to Fig. 16, the con- 
crete bed being 17 ft. 3 in. X 22 ft. 8 ins., somewhat larger than 
drawing : In the e^e-beams, 20,000 lbs. extreme fibre strain is 
allowed, and for the rails, 16,000 lbs. The top course is com- 
posed of 15-in. steel beams, 50 lbs. per foot, whose moment of 



346 A PRACTICAL TREATISE ON FOUNDATIONS. 

resistance is 117,700 ft.-lbs. ; the other courses steel rail, 75 lbs. 
per yard, 4I ins. high and an equal width of base, having a 
moment of resistance of 12,100 ft.-lbs. It is required to find 
the projecting arms of the two upper courses. Those of the 
two lower courses are determined from the lengths of the 
upper ones and the clay areas already determined. 
For the two upper courses 
y = projecting arm ; 
/ = total load ; 

a = width of supported area ; 

M '= total bending moment on one side of the load. 
Then total length of beam = 2y + a, 

y 

Total load on y = I- ' 



2y +a 
and as the load in every course is uniformly distributed, 

M= -4~ X { = Z7^T-k = R - (Eq. 1.) 

2y + a 2 2\2y + a) v -1 / 

In calculating the two lower courses y becomes the known 

and M the unknown quantity. The load on the column is 

1,166,000 lbs. As only nine beams can be put under the 

cast bed-plate, M— R= 117,700 lbs. X 9 = 1,059,300, then 

1,166,000 lbs. X y c . , ., r U 

— ; — : — — = \,o^q,-KOO . y = 5 ft. 4 ins. ; length of beam 

2(27+5) 
— 2jj/-|~5= 15 ft. 8 in. For the third course, M=R = 
12,100 X 31 = 375,100 lbs. This spaces the rails 6 in. centres. 
The load is 1,166,000+ 19,000 (weight of top course and con- 
crete) = 1,185,000.7 = 2 ft. 6 in. The area covered by the 
first course must be 15 ft. n in. X 21 ft. 4 in., giving 3 ft. |- in. 
projection for the first course and 2 ft. 10 in. for the second. 

_, 1,200,000 lbs. X 2f X i T V n/r o -d • • 

Then j ^- = ^=225,780. Requiring 

21-3 

., • 1 1,220,000 X3^tX iff n . 
nineteen rails in course second, and ~-=^ ^- = M 

= 343,000, or, in the first course, twenty-nine rails. Thirty 
were used. The allowable clay loads vary from 1^ to 2 tons. 



FOUNDATIONS FOR HIGH BUILDINGS. 347 

With this load the structure will settle from 3 to 5 ins. After 
carefully laying the rails and concrete the entire exposed sur- 
face is plastered over with cement mortar, so that no part of 
the iron is exposed. (See article in Eng. News, Aug. 8, 1891, 
by C. T. Purdy, C.E.) This form of foundations is probably 
the best practice for high buildings, and therefore it is given 
in some detail. The great advantage of this method is in only 
requiring a small thickness of concrete. The failure of the City 
Hall was due to a too thin bed of concrete and being required 
to act as a beam, owing to the unequal resistance of the clay. 
The building settled unequally, as much as 14 ins. 

The following are examples of loads actually borne : A 
stick 12 ins. square on micaceous sand did not settle perceptibly 
under a load of 10 tons and 8 tons per square foot on screw- 
disks at Coney Island. East River Bridge, 6£ tons on sand. 
In New York approach 1600 feet masonry, 3^ tons to 4% tons ; no 
cracks. Clay under Capitol at Albany, 2 tons per square foot ; 
3 ft. below surface. Bridge at London, on gravel over blue clay, 
5^ tons per square foot, failed after many years. The Washing- 
ton Monument when one third built caused pressure of 5 tons 
per square foot on a mixture of clay and sand, but settled after 
a number of years, \\ ins. out of plumb. The base on resum- 
ing work was spread by cutting channels in under the masonry, 
so as to reduce the pressure to 10,000 lbs. per square foot. It is 
estimated that this pressure is doubled on the leeward side in 
high winds. No evidence of further settling. Public works 
in India do not settle on silt and alluvium with 1 ton per 
square foot ; with 2700 lbs., settled \ inch ; with 2 tons, decided 
settlement. Fort Livingston, Mississippi, built on fine sand, 
20 ft. thick, settled during building 2 to 3 ft., subsequently 1 to 
2 ft. gradually. Government building at Chicago settled dur- 
ing thirteen years 6 to 18 ins. 

Tay Bridge, Scotland, on silty sand, load 3 to 3J tons per 
square foot ; weights added increased the load to 5 and to 5^ 
tons per square foot, remaining from 6 to 25 days, settled 
about \\ to if ins. Exhibition buildings at Paris, gravel rest- 
ing on stiff clay, 6000 lbs. per sq. ft. when the gravel was 10 ft. 



34$ A PRACTICAL TREATISE ON FOUNDATIONS. 

thick, 4550 lbs. when 5 to 10 ft. thick ; when less than 5 ft. 
thick, piles were driven. In one test a load 8 tons per square 
foot, caused a settlement of 1 1 ins. in 12 hours, but 6 tons were 
carried safely. Hudson River Tunnel, on Hoboken side, safe 
load on mud 5580 lbs. per square foot. 

A length of 9 ft. 6 ins. in a wall settled about \ inch with 
a pressure of 62 lbs. per square inch at time of building-, the 
wall being built rapidly. Loading walls too quickly has caused 
bulging. Building masonry with very thin joints on the face 
and thicker joints behind often causes chipping on the face, 
notably Philadelphia Public Building and Washington Monu- 
ment (see Engineering News, Feb. 14, 1S91).* 

The Eiffel Tower: total weight of iron, 7300 tons. The 
total load on foundations is 565 tons, increased to 875 under 
maximum wind pressure. Total height of the tower, 984 ft. 
There are four independent foundations at the angles of a 
square 330 ft. on a side, and each foundation is made up of 
four separate inclined piers. The main foundations are on a 
bed of gravel 18 ft. thick, the top of the bed 23 ft. below the 
surface; these rested directly on a bed of concrete 7 ft. thick. 
For two of the piers the bed of sand and gravel, about 40 ft. be- 
low the surface, overlaid by soft deposits, was reached by the use 
of compressed air, the caisson being sunk 52 ft. to a good bear- 
ing soil. The bed stones under the great piers have a crushing 
strength of 1600 lbs. per square inch ; maximum load that can 
come upon them is 425 lbs. per square inch. The total load on 
each of the two foundations on the concrete bed is 1970 tons. 
The concrete has the following dimensions: 32 ft. 9 ins. X 19 ft. 
8 ins. (= 644.86 sq. ft.) and 6 ft. 6 ins. thick. The load on the 
masonry is about 3 tons per sq. ft. (see Eng. News, June 8, 
1889V 

The City Hall of Kansas City was constructed over the site 
of an old ravine, which was partly filled by the material from 
the adjacent clay bluffs, and in part by the ordinary rubbish 

* This settlement of brick walls and buildings refers to settlement or shrink- 
ing of mortar in joints of masonry either causing settlement of whole structure 
uniformly, or unequal settlement due to difference in thickness of the same 
mortar joint, throwing an excess of pressure on the face, causing chipping. 



FOUNDATIONS J<OJ< HIGH BUILDINGS. 349 

dumped in from the city carts; the fill was 50 ft. deep. Holes 
were bored by means of a large auger 4 ft. 6 ins., worked by 
steam ; an iron cylinder, metal thickness fa in., followed the 
auger down ; when solid bottom was reached the cylinders 
were filled with vitrified brick well bonded ; these bricks had a 
crushing strength of about 135 tons each. 

The Chicago Auditorium Building has a frontage of 362 
ft. Total area covered about 63,000 sq. ft. The building 
proper is ro stories high ; on one of the fronts a tower rises 240 
ft., and 94 ft. above the main building. The foundation of the 
tower covers an area of 69 X 100 ft. The weight on the foun- 
dation-bed, 15,000 tons,= about 4350 lbs. per sq. ft. An ex- 
cavation was made to the clay layer ; on this bed a timber 
grillage, 2 ft. thick, was constructed ; on this, solid concrete 5 
thick was placed ; and to prevent unequal settlement and dis- 
tribute the weight uniformly three layers of rails, one layer 
15-in. V-beams, and one layer 12-in. eye-beams were imbedded 
in the concrete ; and as an additional precaution against the 
heavy, concentrated weight of the towers cracking the ad- 
joining walls a direct load, about equal to its completed load, 
was placed on the tower walls, and gradually removed as the 
walls were carried up. 

Many of the high buildings have foundations of this char, 
acter. Where timber is used great care should be taken to 
place it well below the surface of constant moisture. 

In all of the above examples, except where specially noted, 
the structures have stood, no serious settlement having oc- 
curred up to the time of publication. Many other similar 
examples could be cited, but the above shows the usual loads, 
methods of founding, and nature of the structure, taken from 
many localities, and constructed on many varieties of material. 
The writer constructed the high masonry piers for a bridge 
over the Ohio River on this plan, bedding, 12 X 12 in. Michi- 
gan white pine in the concrete. Whether either timber or 
iron is preserved from rot and corrosion when entirely cov- 
ered in concrete can scarcely be considered as a settled fact, 
though generally accepted and believed. See Plate I. 



350 A PRACTICAL J'REATISE ON FOUNDATIONS. 

77. In the above cases the pressures on the foundations are 
in the main given without any complications or uncertainties 
resulting from fractional resistances on the sides of the struct- 
ures, which exist in the case of pile foundations or those con- 
structed by the open crib or pneumatic caisson. The published 
accounts oi these are liable to be uncertain and misleading, 
both on account of the inaccurate distribution of the total 
resistances between the direct bearing resistance and the 
frictional resistance, which is varying within wide limits, and 
also from the different manner of calculating the actual load 
to be supported. In sinking an open crib or pneumatic 
caisson some engineers deduct from the total weight the 
actual or assumed buoyancy of the displaced water as well as 
that of the displaced earth, and others do not. This results 
in a wide difference in the resultant load to be supported by 
friction and direct bearing. Some uniform method is neces- 
sary for an intelligent comparison or subsequent use in other 
structures. In the case of the foundations of the Cairo 
Bridge, already described, the calculation is made as follows: 

Channel Piers. Tons. 

331,000 ft. B. M. timber at 50 lbs. per cu. ft 6S9.6 

Iron 6S.5 

Concrete. 77.345 cu. ft. at 145 lbs. per cu. ft. 5.607.5 

Masonry, 102, 50S " *' " 150 " " " " 7.6SS.I 

Superstructure 1,027.0 

Moving load 7S5.2 

15,865.9 
Deduct for displacement of 78,000 cu. ft. sand, and 22,756 
cu. ft. water, and frictional resistance at 400 lbs. per 
square foot 9, 5 74. 5 

6,291.4 
Assumed friction resistance 400 lbs. per square foot. 

Fatigue weight 6,291.4 tons = 3. 15 tons per square foot.* 

* In this calculation concrete at 145 lbs. per cu. ft. seems high, 135 lbs. is 
doubtless a good average. Masonry at 150 lbs. per cu. ft. is low for first-class 
masonry, average about 155 to 160 lbs. Timber at 4^ lbs. per ft. B. M. = 50 
lbs. per cu. ft. — 2.09 tons per 1000 ft. B. M. is a fair average. Taking sand 
at 130 lbs., when wet, water at 62! lbs. per cu. ft., then (7S,ooo X 130 + 22,756 
X 62!) = 57S1 tons. .". 9574.5 — 57S1 = 3793o tons for total frictional resist- 
ance. 



FOUNDATIONS FOR HIGH BUILDINGS. 351 

Also for load on concrete base, pier 12 (supposed to be a 
pier on landj : 

'i on», 

12,072 cu. ft. masonry 905.4 

Superstructure 234.6 

Moving load 379-5 

1 519*5 

Or 4.03 tons per square foot. 

The fatigue weight = total weight less displacement and friction. 

From report of Mr. Geo. S. Morrison on the construction 
of the Bismarck Bridge (which contains much detailed and 
valuable information) the following is extracted: Pier No. 4 
on land, excavation in sand to a depth of about 20 ft., and 
piles driven in the bottom. 

Lb». 

28,000 ft. B. M. timber in curb at 4 lbs 112,000 

15,000" " " " grillage at 5 lbs 75,000 

Z64 CU. yds. concrete at 3.510 lbs. (130 lbs. per cu. ft.. . 026,640 
1093.3 '.u. yds. masonry at 4,330 lbs. (160 lbs. per cu. ft. 4,733,989 
257 ft. superstructure at 5,000 lbs 1,285,000 

7,132,629 
Deduct for immersion 11,390 cu. ft. at 62£ lbs 711,875 

Net weight 6,420,754 

[6l piles, average load per pile 39,880 

Also pier No. 2, pneumatic caisson, sunk through water, 
sand, and into a hard black clay. The total weight, as calcu- 
lated in the same manner above, = 17,269,000, and deducting 
for immersion 4,510,000; net weight = 12,759,000 lbs.; area of 
base, 1924 sq. ft.; average pressure per square foot, 6631 lbs., 
or 46 lbs. per square inch. 

In the first case a steam pile-hammer was used in driving 
the piles: depth driven in sand varied from 23 to 34 feet. 
The penetration in the last 10 blows varied from o to 0.2 of a 
foot, or an average for the greater penetration of 0.02 ft. 

Similarly in the Piattsmouth Bridge one of the piers on a 
pile foundation has the following record : Total weight, 
2,114,750 ("apparently no deduction for immersion); number 



35 2 A PRACTICAL TREATISE ON FOUNDATIONS. 

of piles, 78; average weight on pile, 27,112 lbs. The piling 
record is especially interesting. Weight of hammers, 3100 
and 3900 lbs.; average fall at last blow, 28 ft.; average pene- 
tration at last blow about if ins., some few as much as 2 to 3 
ins. ; average depth in the sand, 27 ft. Out of the 78 piles, 8 
broke off under the blows ; 15 piles broke, mashed, and split or 
otherwise injured ; that is, about 10 per cent were broken off 
and about 20 per cent were visibly injured. The number of 
blows ranged from ico to 142 per pile. It can hardly be 
doubted that there were many piles more or less seriously 
crippled below the surface and out of sight. 

The other piers being founded on rock, the pressure per 
square foot is unimportant. They ranged, however, from 4090 
lbs. to 6393 lbs. per square foot. No allowance for nor notice of 
frictional resistance seems to have been allowed for in these 
reports. Although Mr. Morrison deducts for the immersion of 
the structure, he says that this is only done to get the rela- 
tive pressure, that is, the increased pressure on the foundation 
over that on the surrounding surface, "which is the real 
measure of the labor of the foundation." The actual pressure 
is the whole weight of the structure " with the addition of the 
atmospheric pressure." The relative pressure might be useful 
in estimating the bearing resistance at one depth in a certain 
material, knowing the bearing resistance at any other depth, 
provided the law of variation, increase, or decrease was pro- 
portional to the displacement ; but this could only be true in 
a perfect fluid. If this is true no allowance for side friction 
should ever be made. Some engineers do not consider friction 
at all, owing to the fact that it may be in part or entirely 
destroyed by scour. That it does, however, form a very large 
proportion of the actual bearing resistance of many structures, 
and often is the sole reliance cannot be denied. Other examples 
of pressure on foundation-beds have been given in the preced- 
ing pages. 

78. The determination of the frictional resistance on the 
surfaces of piles, cribs and caissons has not been considered 
as carefully as the importance of the subject demands. Favor- 



FOUNDATIONS FOR HIGH BUILDINGS. 353 

able conditions do not always present themselves, and exact 
conditions are not always known, friction during continuous 
motion being different from that developed in starting from a 
condition of rest, and again varying with the period of rest ; 
and often high average surface resistance may result from great 
local resistance at only a few points. The following are a few 
examples of the estimated frictional resistances by different 
engineers, from data and other considerations satisfactory to 
them. But to be convinced of the value and importance of 
friction, endeavor to pull piles and find the power necessary, 
after due allowance for weight of pile, the effect of suction, 
and want of rigidity in the fulcrum, and this too notwithstand- 
ing that smaller cross-sections are being exposed, and only 
after a considerable amount of lift will the pile be raised 
readily and rapidly. On measuring friction of motion by sink- 
ing piles with weights, the loss of frictional resistance is not 
so apparent, as larger surfaces are being pressed where the 
smaller were ; and this largely explains the fact that pile founda- 
tions generally settle only a short distance before a new condition 
of equilibrium is brought about. And as is often stated that it 
is only the initial resistance to settling that is worth consider- 
ing, it is evident that the above-mentioned fact has been over- 
looked. In sinking a pneumatic caisson or crib, as smaller sur- 
faces are being continually presented in the place of larger ones, 
the initial resistance is soon dissipated entirely, and "the ten- 
dency is to continue going when once started. This is entirely 
in keeping with the experience in the Hawkesbury caissons, 
where those without any bottom spread were the more readily 
handled, and gave less trouble. In measuring the resistance 
to sinking caissons, it is the exception, rather than the rule, 
that the compressed air is entirely removed from the caisson.' 
This would reduce the resistance by the air-pressure per square 
inch or square foot. The escape of the compressed air under 
the caisson may materially reduce the outside friction. In 
many cases, however, the air finds a passage of escape at 
considerable distances from the caisson, as evidenced by the 
bubbling of the water at the surface. It is clear, then, that 



354 A PRACTICAL TREATISE ON FOUNDATION'S. 

estimates made on the frictional resistance cannot, under the 
ordinary conditions and manner in which they are calculated, 
be regarded as by any means accurate. But more careful and 
extended observations should be made when opportunities 
occur. The circumstances under which the following estimates 
were made are not known to the writer, except those made by 
himself. It is, however, all that he has, and is given simply as 
stated in Engineering News and other works. Mr. Collinwood 
in the News of Feb. 21, 1891, states that in sinking brick wells 
5 to 18 ft. diameter to a depth of 50 ft. or more, a load of 300 
tons was required ; in the alluvium in India the " skin friction" 
was from 500 to 1500 lbs. per square foot. At the Dufferin 
Bridge it was 1000 lbs. for wells 12^ ft. in diameter. On the 
caissons of iron of the St. Charles Bridge, sunk through 20 ft. 
of bowlders, the friction was 466 lbs. per square foot. The 
caissons of wood, East River Bridge, gave about 900 lbs. in 
bowlders, clay, and sand, and in clear sand from 400 to 600 lbs. 
per square foot. And in case of iron caisson for a lighthouse, 
200 lbs. per square foot. 

In the case of caisson No. 2, Susquehanna River, sunk under 
the writer's supervision : Indicated air-pressure of 33 lbs. This 
was reduced to 26 lbs. in order to sink the caisson under a total 
weight of 9,356,760 lbs.; deducting the buoyant effect of the 
air = 6,143,904 lbs., the net weight to overcome resistance = 
3,212,856 lbs., giving 33 \\ lbs. per square foot of exposed sur- 
face in sand. A subsequent test gave 380 lbs. per square foot. 
At this depth the caisson had entered into a layer of bowlders 
which continued as far as the caisson was sunk, 68' 4" below 
low water, about 55 ft. through a rather clean sand and under- 
lying bowlders. The material was entirely removed from under 
the caisson, and it was held by friction alone. The only source 
of error in the last case (380 lbs.) was inaccuracy in the pressure- 
gauge. The indicated pressure was reduced to that due to the 
depth ; this was done as in ordinary sand and gravel it is diffi- 
cult to maintain a pressure greater than that due to the depth. 
On account of leakage, had a similar reduction (5^ lbs., gauge 
36 lbs. ; depth below water about 60 ft. ; estimated actual press- 



FOUNDATIONS FOR HIGH BUILDINGS. 355 

ure 30J lbs.) been made in the first case, the two records (33 i-J 
and 380 lbs.) would have been nearer together, as they should 
have been. The weights were the same, and the depths being 
44^ and 47 ft., respectively. In sinking caisson No. 3 the two 
records show at a depth of about 40 ft. below the bed of the 
river in good grained sand, weight 8,465,871 lbs. ; buoyant 
effect of air, 6,032,989 lbs., reduced weight to 2,432,882 lbs. ; 
area of surface below the bed of the river, 8533 square feet; 
hence friction resistance per square foot 285 lbs. When 46^- 
ft. down record shows 379 lbs., having entered the bowlders. 
The caisson was sunk about 4 ft., and building commenced on 
the bowlders. Depth below bed of river 50' 8f ". Total below 
water surface 70' 8f ". 

At caisson No. 4, depth of water, 28 ft. at low-water ; 
depth of solid material to highest point of rock, 31' \o\" ; to 
owest, 37' 3^" ; which was a compact silt, air-tight and water- 
tight, but easily forming mud or slush when mixed with water. 
When the caisson first rested on the bottom (as it had a false 
bottom for launching ; none of the other caissons had one), it 
rested easily, but sunk 3.3 ft. while cutting out false bottom. 
The ordinary weighting with timber and concrete was sufficient 
to sink the caisson into the bed about 14 ft. by only reducing 
the pressure about 3 lbs. ; and when the cutting edge was 
57.5 ft. below water, or 29.5 ft. in the silt, the caisson settled 
under a reduction of only 1 lb. in the air-pressure, showing a 
nice adjustment between weight and resistances. At this depth, 
total weight 10,958,448 lbs.; upward pressure of air, 9,014,907 
lbs.; resistance to sinking, 1,943,541, giving 308 lbs. per square 
foot. In settling 1.3 ft. farther, one edge of the caisson rested 
on rock ; and as the caisson was out of level about 15 inches, the 
rock was blasted off along this end ; then reducing the pressure 
to level the caisson, the frictional resistance was apparently 
489^ lbs,; but the caisson was blocked against the soft mate- 
rial on the lower side of the caisson to prevent settling there ; 
this record is then too high. The caisson was stopped at 
65' 3i"« below low-water; the excavation carried on, without 



35^ A PRACTICAL TREATISE ON FOUNDATIONS. 

difficulty, below the cutting edge to rock on all sides. Great- 
est depth to rock, 69/ io£". 

In caisson No. 8, depth of water 29 ft.; of soft silt at high- 
est point of rock, 47 ft.; at lowest, 59.34 ft. Caisson was only 
sunk 3 or 4 ft. into rock at highest point. Excavation carried 
on below cutting edges, exposing rock over whole area. Least 
depth below low-water, 76 ft.; greatest, 88.34 ft. Owing to 
the large size of this caisson, the softness of the silt, and ap- 
prehension of trouble, the material was never removed entirely 
from under the caisson ; in fact, it was sunk resting on block- 
ing to a great extent, so it was impossible to estimate the fric- 
tional resistance with any degree of accuracy. The caisson 
sunk almost continuously, although concreting was stopped 
when within 29 ft. of the rock, the only extra weight being 
the necessary timder to keep the top above water as the cais- 
son settled. The frictional resistance could not have ex- 
ceeded 200 lbs. to the square foot, owing to the slimy nature 
of the material passed through. The depth below high tide 
would be about 92 ft. The other depths for caissons 2, 3, and 
4 should also be increased by the same amount, as this latter 
was the depth for which air-pressure had to be provided every 
day. In high winds the tides would be either very high or 
very low. The following observations were made in sinking 
the caissons for the Cairo Bridge : 

Penetration in sand, 86.42 ft.; below water surface, 90.27 ft.; weight of caisson, 
887 tons : crib, 3163 tons ; masonry, 2800 tons ; weight of sand and 
water, 1806 tons ; total, 8656 tons. 

Indicated air-pressure before sinking 42.75 lbs. 

Calculated" " " " 39.117" 

Indicated " " " when lowered ... . 36.00 " 

Air-pressure 42.75,39.117, 36.00 " 

" " reaction due to 4,802, 4,394" 4,044 tons 

Net weight 3,854, 4,262, 4,612 " 

Exposed surface of caisson 12,910, 12,910, 12,910 sq. ft. 

Frictional resistance 597, 660 715 lbs. per sq. ft. 

However, in finding the " fatigue " weight (see par. jy) y 
or pressure on the foundation bed = total weight — deductions 



FOUNDATIONS FOR HIGH BUILDINGS. 357 

for displacement of sand and water and frictional resistance 
on exposed surface of caisson, they only allowed 400 lbs. fric- 
tion per square foot. Assuming wet sand to weigh 140 lbs. 
per cubic foot, and water 62^ lbs., we find the weight of the 
displaced material = 78,000 X 140 lbs. -\- 22,756 X 62J X 62^ 
= 6171 tons, and side friction = 95745 — 6171 tons = 3403.5 
tons, which would give, at 400 lbs., 17,017.5 square feet of sur- 
face in that case. The data is not given, but this shows the 
method of calculation adopted. 

79. There seems to be very few records in regard to the 
frictional resistance on the surface of piles. In what is in fact 
a liquid mud the resistance to settling has been fully shown to 
be not less than 130 lbs. per square foot, and in compact silts 
and clays 200 to 250 lbs. would not be excessive, though not 
based upon actual experiment. As in sinking caissons, which 
would certainly give minimum values for the reason stated, 
300 to 400 lbs. per square foot is a fair resistance, and as this 
increases as piles settle, we can safely allow from 300 to 500 
lbs. for piles in sand and gravel. 

In a letter from the city engineer of New Orleans he states 
that the soil is alluvial — a sandy clay saturated with water at 
a depth of three or four feet. Allowing 1000 to 1500 lbs. per 
square foot, if the spread is not more than ten bricks, the brick 
wall is simply started on the bottom of the trench. If piles 
are required, they are driven 4 ft. centres and capped with 
a four-inch floor, upon which the brick-work is started. 
Piles from 25 to 40 ft. long will carry from 15 to 25 tons, 
with a factor-of-safety of 6 to 8. Taking, then, a pile of 
25 ft. into the ground, and assuming average diameter 12 ins., 
having then 3 square feet to the linear foot, or 75 square 
feet of surface, the direct bearing being taken at 1500 
lbs., the safe load on the pile will be 15 X 2000=30,000 
lbs., or to be carried by friction, 30,000— 1500=28,500 lbs., 
and frictional resistance per square foot will be 380 lbs., and for 
the 40-ft. piles 405 lbs. per square foot. This is in excess of 
the suggested allowance by 405 —250=155 lbs., for such 
material. 



358 A PRACTICAL TREATISE ON FOUNDATIONS. 

The enormous grain elevators in Chicago rest upon pile 
foundations. Mr. Adler states that the unequal and constantly 
shifting loads are a severer test upon the foundations than a 
static load of a 20-story building. Taking the load on the steel 
and concrete piers already illustrated, the concrete bed is 17 ft. 
3 in. X 22 ft. 8 ins. ; with piles 2.8 ft. centres we could get six 
rows of nine piles each = 54 piles ; with 3 sq. ft. per linear foot 
a 50-ft. pile would expose 150 sq. ft. of surface at a frictional 
resistance of only iOO lbs.; each pile would carry 15,000 lbs., 
and the 54 piles would carry 810,000 lbs. On the concrete and 
steel foundation the load is 800,000 lbs.; at 2^ ft. centres about 
70 piles could be driven in the same space. With the low 
limit of J7 lbs. per square foot a 50-ft. pile would carry 11,550 
lbs., and the 70 piles 808,500 lbs. With the knowledge that we 
have there can be but little doubt, if any, that a pile founda- 
tion will carry any loads yet put upon the soil underlying the 
city of Chicago, if properly arranged and driven. 

80. The reader will have learned, if he has even casually 
glanced over this volume, that engineers and architects are 
far from agreement as to the mode of determining the bear- 
ing power of any of the materials upon which we have to 
build ; we are far from agreement as to the safe loads that can 
be put upon them or the proper manner of distributing the 
loads. In such cases arguments are useless ; high-sounding or 
ingenious formulae are of but little value. Theories will not 
solve the problem. 

What we need is systematic, honest, extensive experiments 
and tests, and with these, honest, impassionate interchange 
of ideas and deductions, without petty jealousies or fault-find- 
ing. With rigid but kindly criticism of designs and of methods 
of construction, we might hope to advance our knowledge, 
improve our practice, and give the public safe, substantial, and 
satisfactory results, at the least cost and in the least time. 

In writing this volume the writer has endeavored to avoid 
putting forward pet plans or theories. If prominence has been 
given to designs, it is only because he believed them as good as 



FOUNDATIONS FOR HIGH BUILDINGS. 359 

those of others, and was more familiar with their details ; and 
with simple alterations in some of the details they are typical 
of all such structures. He has commented on the designs of 
others, expects such criticisms of his own, as only in this way 
can we hope to arrive at the truth. 



CONCLUSIONS. 

81. The increasing demand for high buildings, owing to the 
contracted areas upon which buildings must be erected and 
the enormous cost of the same, has naturally led to much dis- 
cussion, many eminent engineers and architects claiming that 
the limiting height and consequent weight per square foot of 
bearing surface has been reached. An additional spread of 
base beyond that now attained is impossible on account of the 
contracted areas and also on account of the rights of abut- 
ting property-owners. And that owing to the already great 
unit pressures on the usual foundation-beds of sand, gravel, or 
clay, which, although they now apparently safely carry their 
loads without any but a very small and allowable settlement, 
yet such structures may be regarded as in a precarious condi- 
tion if subsequent operations of abutting property-owners, 
such as tearing down existing buildings and excavating to 
greater depths, either for increased cellar room or to secure 
better and stronger foundations, should remove lateral support 
from the foundation-bed of an adjacent building. The result 
would be a flow or bulging of the material, and thereby causing 
serious cracks or other permanent injury to the building. 
Especially is this a living danger if the material is a water- 
bearing sand or silt. 

82. The substitution of piles as a means of spreading the base 
or acquiring increased bearing resistance is advocated by many 
equally eminent engineers and architects, backed by many 
well-established precedents. On the contrary, however, ex- 
amples of structures on pile foundations are not wanting to 
show that, for some not explained or inexplicable reason, after 



360 A PRACTICAL TREATISE ON FOUNDATIONS. 

carrying a load for years with perfect safety, such foundations 
have ultimately failed, causing either a partial or complete 
wreck of the structure. 

Whether or not pile foundations are any better, so far as 
affording direct support is concerned, may be a matter of rea- 
sonable dispute and difference of opinion, as piles may be 
badly injured in driving, their upper portions may not be 
driven below surfaces of constant moisture, or, if so driven, 
the superincumbent weight may lower the level of this water- 
surface ; or subsequent systems of drainage, or even natural 
subsidence of the surface, may occur, exposing the piles to 
conditions of alternate wetness and dryness, resulting in the 
piles rotting and consequent failure of the structure. A case 
of this kind occurred under the tower .of a market-house in the 
city of Richmond. The building was badly cracked. Col. W. E. 
Cutshaw, City Engineer, on excavating below the structure 
found that it had been originally built on piles, which had 
rotted to a considerable extent and depth below the surface. 
After forcing the walls back, closing thereby the cracks to a 
great extent, and supporting them in this position with jacks 
and props, he excavated under the walls and filled the trench 
with a carefully made cement concrete, rammed in layers, which 
were allowed to partially set as the work progressed, so that 
when the concrete was rammed under and against the old 
walls the entire mass had a good set. Subsequently the props 
were removed, throwing the entire weight on the concrete. 
No further trouble has occurred. 

83. Although this and similar cases show the uncertainty, 
under some conditions, of pile foundations, they are used to ,a 
great extent with entire satisfaction, and will certainly to a 
very great extent do away with the danger of the material 
flowing or bulging from under a structure by removing the 
weights from or excavating in adjoining lots. 

We have, then, open to the builder for selection: 

1st. Simply building the foundation walls or pillars on the 
natural bed, spreading the base with projecting courses of 
masonry. 



FOUNDATIONS FOR HIGH BUILDINGS. 3 61 

2d. Obtaining the necessary spread with a timber platform 
or grillage. 

3d. Driving piles, either to some hard or firm material or 
to rock. 

These two methods may cause settlement by rotting of the 
timber. 

4th. Building the walls upon beds of concrete of sufficient 
area, either alone or strengthened by iron or timber beams 
built in the concrete. 

5th. Sinking cylinders of iron or caissons of timber or iron 
of such dimensions as to support either a single column or a 
series of columns or walls, these caissons being sunk either to 
rock or to such a depth and material as will preclude the pos- 
sibility of failure occurring from any of the above-mentioned 
causes. 

84. Two notable examples of this last method are found in 
the City Hall of Kansas City, in which case cylinders were sunk 
to rock, as explained, and the new pump-house of Louisville 
Water-works, which is erected on a large timber caisson sunk 
by the pneumatic process, a single caisson of sufficient dimen- 
sions for the entire building to rest on being used. 

85. A somewhat new departure in this direction will be 
found in case of a large building, the Manhattan Life Building, 
shortly to be erected in New York. Sooysmith & Co. are the 
contractors, and they have kindly sent me in advance of the 
commencement of the work, or even the construction of the 
caissons, the following facts and data. My excuse, if any is 
needed, for inserting any account of a foundation not even 
commenced in a work on foundations is the perfect assurance 
that the work will be carried to a satisfactory completion, 
whatever may be the difficulties or costs involved, by the 
contractors. 

Depth to bed-rock is 50 ft. below the level of Broadway 
and 25 ft. below the cellar floor, which is even with the natural 
water-level. The caissons will be sunk by the pneumatic 
process through sand and quicksand. There will be fifteen 
caissons built of boiler-plate steel. Four (4) of the caissons 



362 A PRACTICAL TREATISE ON FOUNDATIONS. 

will have circular cross-sections, varying from 10 to 15 ft. in 
diameter. The remaining eleven (11) caissons will be of rec- 
tangular cross-section, ranging in size from 13 to 26 ft. square, 
some of them being 10 ft. X 26 ft. in dimensions. The roof 
will be strengthened by 1 5-in. eye-beams. The piers will con- 
sist of hard-burnt bricks laid in Portland cement, capped with 
several courses of granite, stepped off to a proper size to re- 
ceive the bed-plates for the iron columns, some of which will 
support as much as 1500 tons. 

The entire number of caissons will be put in place at once 
and the brick-work commenced on them. Several will be 
sunk at the same time. It is the intention of the contractors 
to sink these caissons with a weight sufficient to overcome 
both frictional resistance and the buoyant effect of the com- 
pressed air, and not to sink, as is ordinarily done, by reducing 
the air-pressure. The object of this is to prevent the large 
inflow of sand and gravel which usually takes place when the 
air-pressure is reduced. 

It is highly probable that this can be accomplished, as the 
depth to be sunk is not very great, and both the total frictional 
resistance and upward pressure of air will be relatively small. 

At very great depths in sand and gravel it becomes often 
difficult to sink the caisson, even with greatly reduced air- 
pressure, and in many sands and gravels more or less inflow 
of the material takes place even against the air-pressure, espe- 
cially if the excavation is carried at all below the cutting edge. 
At least this is the writer's experience. The ability and 
experience of the contractors will, however, enable them to 
contend successfully with any difficulties likely to arise. 

The entire question, heretofore, of applying this method 
to ordinary buildings has been one of actual and relative 
rapidity and cost in the construction. If these difficulties can 
be removed, there can be no question of the advisability of 
adopting this method for all important buildings, even if the 
necessity, from a practical point of view, does not require it — 
certainly when rock is at no very great depth below the sur- 
face, as the feeling of perfect safety as well as the demand 



FOUNDATIONS FOR HIGH BUILDINGS. 363 

for it will justify the increased cost, provided it is not too 
large a percentage of the entire cost of the structure. And as 
buildings become more costly the smaller will be the percentage 
of cost for the foundation, and the greater is the reason, purely 
from a selfish or economic point of view, to make the founda- 
tions absolutely safe and secure, to say nothing of the greater 
danger to the comfort as well as to the life of the occupants, 
which imposes a far larger responsibility on the builders. 

86. In this connection the relative advantages, both as 
regards rapidity and cost of construction, of sinking wells for 
foundations, which is done successfully in India to a great ex- 
tent, and to which allusion has already been made, may be 
discussed. An interesting construction of this kind has been 
only recently completed, an account of which will be found in 
the Engineering News of January 12, 1893. These foundations 
were for the piers of a bridge on the Madras Railway, India. 
The method, however, is equally applicable to the foundations 
of high buildings where it is desired to reach bed-rock. The 
spans for this bridge were about 140 ft. long. The masonry 
for the abutments and piers above a certain level was lime- 
stone, resting on foundations obtained by well-sinking. 

The plan of the abutment was of the usual form, with face 
wall and splaying wings. Seven masonry wells resting on 
curbs were sunk to rock 57 ft. below the bed of the river- 
three wells under the face wall and two under each wing. 
The external diameter of the well was 12 ft. where it rested 
on the curb, and for a height of 20 ft. above, where it was 
reduced to 1 1 ft. diameter. The walls of the well were built 
of limestone masonry laid in mortar. In one of the wells, 
sunk 40 ft. through clay, one side rested on masonry of an 
adjacent well, and the other side on a curb of another adjacent 
well, but the excavation was carried down between the wells 
to the bed-rock, and the space refilled with concrete. The 
entire enclosed space in all of the wells was filled with Port- 
land cement concrete. The thickness of the walls of the wells 
is not given, but assuming from 2% to 3 ft., the diameter of the 
enclosed hollow space would be from 7 to 8 ft, and about 5; 



3°4 A PRACTICAL TREATISE ON FOUNDATIONS. 

ft. long. Arches were then sprung from cylinder to cylinder, 
and the solid masonry built on the arches. The piers were 
constructed by sinking two cast-iron cylinders, 12 ft. in diameter, 
for each pier placed 18 ft. centre to centre. These cylinders 
were from 40 to 47 ft. high, reaching from bed-rock 55 to 62 
ft. below the bed of the river, to a point 15 ft. below the bed. 
At this point the diameters were reduced by a conical taper 
7 ft. 6 ins. high to 9 ft., and carried to full height at this 
diameter. These were finished on top with a sliding cap and 
connected by wrought-iron massive bracing-boxes, bolted and 
filled with concrete. To facilitate the sinking of the cylinders 
at a point 12 ft. above the cutting edge brackets 2 ft. 9 ins. 
wide were fastened to the cylinders, on which a masonry wall or 
lining was built up to a point at the middle of the length of the 
conical taper. This really converted the cylinder proper into a 
masonry well with iron casing, reducing the external frictional 
resistance. The hollow spaces in all cylinders were then filled 
with concrete. Above the top of these wells or cylinders solid 
masonry was built to the top of the pier, below the bed of the 
river in cement mortar, and above in " surki " mortar; The total 
depth sunk, of cylinders and wells, was 2364 ft. The cost for 
the cylinders was $14,170, and for the wells $11,630, including 
charges for bedding on the rock performed by divers. Total 
cost, $306,402, or $146 per linear foot of bridge, which was 
2100 ft. long. The iron in the cylinders cost $85,142, and in 
the girders $110,000, or total cost of iron $196,410 (as given 
in report) ; leaving for the masonry lining, concrete rilling, 
and sinking of the wells and cylinders $109,992, or per linear 
foot of cylinder $46.50. This last calculation is made by the 
writer, as he understands the data given above. 

87. Also for the end piers of the Kentucky and Indiana canti- 
lever bridge across the Ohio River at Louisville, brick-lined 
cylinders of iron were sunk and subsequently filled with con- 
crete, constituting a similar construction to the above. The 
pier on the Indiana side, carrying one end of a 240-ft. through- 
span, was composed of two plate-iron cylinders, metal thick- 
ness f in., in sections, riveted together as the work progressed. 



FOUNDATIONS FOR HIGH BUILDINGS. 3 6 5 

The brick lining rested on a shoe or cutting edge at the bottom 
about i ft. high ; the thickness of the brick wall was 18 ins. for 
a height of about 6 ft.; the thickness was then reduced to 13 
ins., and continued at that thickness to the top. The cylinders 
were sunk simply by excavating the material on the inside, 
and building the cylinder and brick-work at the same time. 
After reaching the proper depth, the hollow inclosed space was 
filled with concrete. The interior diameters of the cylinders at 
the bottom were 10 ft. ; exterior diameter, 13 ft. of in. ; at top 
interior, 7 ft. 6 in. ; exterior diameter, 9 ft. 8| in. The exca- 
vation was carried down in the rock 5 ft. below the cutting 
edge. The following is the cost of this pier : 

2 cylinders f-in. iron, 105,662 lbs. at 5.72 cts $6,043 87 

504.0 cu. yds. earth excavation inside of cylinder at 75 cts.. 37S 00 

144.2 " rock " •' " $1.50.. 216 30 

170.28 " brick-work in lining at $11 1,87308 

299.75 " concrete filling at $6 1,7985° 

9.72 " coping at $20 194 4° 

6.5 " cut backing at $6.60 4290 

Sundries 78 59 

420.0 cu. yds. earth filling around cylinders at 25 cts 105 00 

Total for two cylinders $10,630 64 

And for each cylinder $5315.32 ; the total length being 75.9 ft, 
or per linear foot of caisson $70.03. The engineer in charge, 
Capt. C. A. Brady, who has kindly furnished me with the 
above and the following data, informed me that the rock exca- 
vation was entirely unnecessary, as it was a hard, compact 
slate, which would reduce the cost per foot of length to $57.69. 
The two cylinders for the pier on the Kentucky side were 
larger, carrying the projecting arm of the cantilever span 260 
ft. long, as they also acted for an anchorage pier. Bottom 
diameter 15 ft. 5| in. exterior, and 11 ft. at top, lined similarly 
to the above-described cylinders; total length 112.2 ft. ; weight 
of iron in two cylinders 153,081 pounds. The unit prices 
same as above ; quantities considerably increased. Total cost 
$18,498.36 for the two cylinders, for each $9249.18, and cost 
per linear foot $83.32. These cylinders were sunk through 



3 66 



A PRACTICAL TREATISE ON FOUNDATIONS. 



KENTUCKY AND INDIANA BRIDGE 
PIER No. 9. SECTIONS OF EAST CYLINDER. 

Showing final position and adjustment. 




Fig. 17. — Anchorage Pier for Cantilever. Cvlinders Settled out of Line ; Adjusted 
to Proper Position with Inclined Plates. 



FOUNDATIONS FOR HIGH BUILDINGS. 



3fy 



28 ft. clay, 5 ft. of gravel, and 26 ft. of quicksand, or a total 
depth below the surface of 63 ft. Owing to caving in of the 
quicksand, letting the material down from above, the cylinder 
was thrown out of position ; much additional labor and cost 
was required in removing material, pumping and straightening 
cylinders, adding largely to the cost of the foundation above 




N n 

Fig. 18. — Kentucky and Indiana Bridge Plan of Cylinders. 

an ordinary case. The cylinders were not finally straightened 
at all. To bring the top into position it was necessary to 
rivet a slightly inclined elbow, as shown is Figs. 17 and 18. De- 
tails of the anchorage connections are shown in Fig. 17, near 
the top. These last cylinders are considerably larger than 
those used in India, but the difference in cost is also very 
great. Such costs may be almost prohibitive for ordinary 
foundations for houses. 



SUPPLEMENT. 



THE HAWARDEN BRIDGE. 

88. THE Hawarden Bridge over the river Dee, in Eng- 
land, consists of two fixed spans 120 ft. each and of one draw- 
span 287 ft. end to end. The clear opening on one side of the 
pivot pier is 140 ft. and on the other 87 ft. It is a double-track 
bridge, with a (4) four-foot-wide footway on one side. The 
piers are brick and concrete lined cylinders. The wrought- 
iron cylinder for the pivot pier was built of £-in. plates 
riveted together, having a special rolled section of iron, form- 
ing the actual cutting edge, inserted between them. These 
plates rise vertically for a height of 9 ft. outside ; but. inter- 
nally they slope upward toward the centre of the cylinder, 
until at a height of 9 ft. above the bottom edge the internal 
diameter is 30 ft, the diameter of the bottom or cutting edge 
being 43 ft., the reduction being 6% ft. all around, forming a V- 
shaped curb or section 9 ft. high and 6|- ft. wide at top. 
This section was filled with cement concrete made 5 to 1 after 
being sunk on the bed of the river. Upon this bottom section 
two concentric cylinders made of iron plate were built to a 
height of 15 ft., making a total of 24 ft. in height above the 
. cutting edge ; this was sufficient to reach from the bed of the 
river to above high-tide line. The cylinder was then sunk in 
its proper place, about 200 tons of concrete being placed in 
the annular space between the two plate-iron cylinders. The 
width of this annular space was reduced to about 5 ft. above 
the V-shoe or section, and in it, resting on the concrete, a 
cylindrical brick wall 5 ft. thick was built, the internal diameter 

369 



3/0 SUPPLEMENT. 

being 30 ft. and the external diameter 40 ft. This brick wall was 
carried well up above the water surface. Dredging was then 
commenced inside the cylinder, using the clam-shell dredge. 
As the material was removed and the brick walls were built up 
above the iron casing, the cylinder gradually sank. Except that 
the iron plating was only carried to the height of 24 ft. above 
the cutting edge, — the hollow brick cylinder having no sheathing 
above that point outside nor inside, and that the brick walls 
were 5 ft. in thickness and diameter 40 ft. out to out of wall, 
— the general construction was the same as described for the 
cylinders of the K. and I. bridge described in paragraph 87, 
Part III. 

When the excavating and sinking commenced, the weight 
on the cutting edge was about 6 tons per linear foot. The 
cylinder was sunk to a depth of 48 ft. below the bed of the 
river. With a weight of about 2300 tons the caisson could be 
controlled easily by careful and skilful handling of the clam- 
shell dredge, aided by pumping water under the cutting edge. 
The cylinder was sunk mainly through sand, but if it rested at 
any point on bowlders or lumps of hard clay or other material, 
it was found easy to remove these by pumping water under 
them. This latter process was also found greatly to reduce the 
frictional resistance on the surface of the iron or brick work. 
This same effect was referred to in discussing pneumatic caissons 
as due to the escape of the compressed air under the caissons 
and rising along its outer surface. After reaching the proper 
depth below the bed of the river, concrete was lowered in 
"pigeon-trap" boxes through the water inside of the brick 
cylinder and deposited at the bottom ; this was continued un- 
til its depth was about 18 ft. The concrete was made with 
strong cement, in the proportions of 5 to 1. When this mass 
of concrete had set, it was found practicable to pump the 
water out of the cylinder, and the rest of the concreting was 
deposited in the dry. This concrete was mixed 6 to 1, and 
filled the cylinder to a height of about 65 ft. above the bottom ; 
then a floor of brick-work in cement was laid over the whole 
surface, on top of which was placed a large granite block, 9 ft. 



SUPPLEMENT. 37 1 

square and 3 ft. thick, for the central pivot-bearing, and also 
the masonry for the circular track. This is probably the largest 
cylinder ever sunk under the brick-well system so common in 
India. The cement mortar used in the brick-work seems to 
have been mixed in the proportions of i£ to 1 for the lower 
portion and 3 to 1 for the upper portion. 

For the other piers two cylinders were used, each cylinder 
beiir>- about 12 or 14 ft. outside diameter and 6 or 8 ft. inside 
diameter, allowing brick walls of about 3 ft. thick. These were 
sunk to the proper depth and filled with concrete, as in the 
pivot piers. Three cylinders were used in one of the piers. 
Brick arches were then built, connecting the cylinders at the 
tops. 

The necessary piles for fenders and other purposes were 
sunk by aid of water jets. A 2-in. pipe was temporarily spiked 
to the side of the pile, which was then placed in position ; the 
pipe was then connected to the steam-pump by a flexible hose. 
The water forced through it discharging at the foot of the pile, 
caused it to sink with any desired degree of rapidity. During 
the operation of sinking the pile was easily moved or turned 
into any position. When the pile had reached the proper 
depth the pump was stopped, pipe and hose removed, and 
then fastened to another pile. By this method piles were sunk 
in sand to the depth of 20 to 25 ft. in two minutes, "without 
the delay, uncertainty, or damage which so frequently accom- 
pany the ordinary system of pile-driving. Sometimes a nodule 
of clay or erratic bowlder of the glacial drift was encountered 
by the pile, but by sinking another pipe down to the under side 
of the stone or nodule, and pumping, the obstruction sinks 
away in advance of the pile, which rapidly follows. Within a 
half of an hour of the pumping being stopped the sand settles 
around the pile, and no amount of ordinary pile-driving will 
stir it a fraction of an inch." 

The total cost of this bridge was $355,000, — equivalent to 
$545 per linear foot. No division of this amount between the 
substructure and superstructure is made in the description from 
which the above is taken. 



372 SUPPLEMENT. 

89. FOUNDATIONS AND FLOORS FOR THE BUILDINGS OF 
THE WORLD'S COLUMBIAN EXPOSITION. 

On the subject of foundations for the buildings of the 
World's Fair at Chicago, Mr. A. Gottlieb has made an interest- 
ing report, which was published in the Engineering News, from 
which the following facts are taken. 

Chicago Subsoil. — Commencing at the surface and proceed- 
ing downward, the following lay and thickness of strata are 
recorded in some of the many soundings made, among which 
there were considerable variations : Upper surface black soil, 
then sand 5 to 8 ft.; quicksand 4 to 10 ft.; soft clay 6 to 10 ft.; 
soft blue clay 6 to 10 ft.; blue clay ; hard blue clay ; hard-pan. 
Average depth to hard-pan 26 to 36 ft. below surface. 

The sand, when loaded with 2\ tons per square foot, settled 
f in., and very uniformly, and after this there was no further 
appreciable settlement. On sand filling over mud holes a load 
of \\ tons per square foot settled from 1 to 3 ft., and kept sink- 
ing with the continuance of the load on the platform. In such 
places piles were driven. Whereas on the regular bed of sand 
a load of about 1^ tons per square foot was allowed. The plat- 
forms supporting the columns of the structures were constructed 
of several layers of plank and solid timber scantlings, having 
sufficient top dimensions for the bottoms of the columns to 
rest upon easily, and spreading outwards and downwards, so that 
in all cases the area of the bottom of the platforms should be 
great enough to limit the pressure to \\ tons per square foot of 
surface. He also gave some interesting experiments on the 
resistance of timber columns under compression, as well as the 
resistance to crushing of timber across the grain, recommend- 
ing the safe unit loads to be used. These were not, however, 
materially different from the safe loads already given in this 
volume. 

MAXIMUM AIR-PRESSURE IN PNEUMATIC CAISSONS. 

90. It has been stated that the limit of depth in the pneu- 
matic process has been generally accepted as ioto ft. below the 



SUPPLEMENT. 373 

water surface. The writer has also ventured to express the 
opinion that, with due care and reasonable precautions in select- 
ing men and providing for their comfort and health, greater 
depths could be reached with safety. We have also seen 
that in the St. Louis and Memphis bridges the depth or 
immersion below the water surface reached 108 or 109 ft. 
Many lives were lost in the sinking of the St. Louis caissons. 
No report has been made on the other in regard to this point, 
so far as I have been able to find out. In the Engineering 
News of March 16, 1893, it is stated that a tunnel is now being 
constructed 8 X 10 ft. in cross-section, by the East River Gas 
Company, which will be half a mile long when completeo. 
The headings of this tunnel are now 500 ft. out from the New 
York side and 100 ft. out from the Long Island end. The 
men have worked in compressed air at the respective depths of 
134 ft. and 147 ft. below mean low tide. The men work in 
four-hour shifts. Thus far, one foreman has died and three 
workmen have been brought out unconscious. It is not stated 
what precautions, if any, have been taken for the health and 
comfort of the men. 

Even as matters stand, the percentage of death and paralysis 
or unconsciousness would not seem to compare unfavorably 
with that in many preceding caissons when sunk to much less 
depths and requiring less intensity of air-pressure. 

SOUNDINGS AND BORINGS. 

91. The importance of accurate and thorough soundings 
or borings, in order to determine the character and lay of the 
strata underlying the bed of the river at any bridge site, has 
been earnestly urged in the first part of this volume. (See Art. 
33, paragraphs 25, 26, 2 1 /.) In the Engineering News of April 
13, 1893, is found a very instructive description of the removing 
and subsequent rebuilding of a pivot pier of a bridge over 
the Coosa River at Gadsden, Ala., which had badly settled 
on one side, "the pivot going down stream about 7 ft. and 
nearly throwing the swing-span into the river. The accident 
occurred at «m extraordinarily high stage of water, the river 



374 SUPPLEMENT. 

being subject to a rise of nearly 40 ft. at this point." From 
the description and the accompanying drawings, it seems that 
there was a depth of 12 ft. of water at ordinary low stages, 
and 4 ft. of gravel, overlying the solid rock. The layer of 
gravel, it is stated, was " so compact, indeed, that it had 
proved impenetrable to the sounding-rod of the engineer 
originally in charge of the bridge, and was supposed by him to 
be solid rock." From this statement we are led to infer that the 
sounding was made with an ordinary straight rod, which was 
struck with a hammer or maul in order to determine the nature 
of the material at the bed of the river. That it is difficult, if 
not impracticable, to drive an inch or an inch and a half rod 
to any great depth in a compact bed of gravel or even sand 
is readily admitted ; but that it would not penetrate at all, but 
would give a rebound and a sound easily recognized when a rod 
is simply lifted and dropped on solid rock, cannot be so readily 
admitted. If only one sounding was taken, the rod may have 
rested on a bowlder of large size ; several soundings, however, 
would certainly have determined the question. It was cer- 
tainly unwise to have sunk an open caisson, to simply rest on 
the bed of a river subject to such sudden and great floods, 
without a thorough examination of the nature of the bed. 
The driving of a single pile would have settled the doubt ; and 
again, it would seldom be found that the bed of a river, if solid 
rock, would be sufficiently level to sink a solid bottom caisson 
on it without some careening. The bed being practically 
horizontal, should have at least aroused a suspicion that the 
bed was either gravel, sand, or clay. At the depth given — only 
twelve feet of water — it would seem that an ordinary coffer-dam 
should have been used, in which event the treacherous nature 
of the bed would have been discovered, a good foundation 
secured, and the subsequent danger and cost avoided. Had 
the soundings been made by the use of pipes and a force-pump 
the existence of the gravel bed would have been determined. 
(See Art. 33, paragraphs 25, 26, 27 ; and also Plate IV, Fig. 10.) 
The height of the pier was about 80 ft., and it contained 
1 100 cu. yds. of masonry. As the pier had to> be removed 



SUPPLEMENT. 375 

entirely, a large coffer-dam had to be built around the pier. 
"This dam gave a great deal of trouble during the prosecution 
of the work, owing to the porosity of the gravel and to the irreg- 
ularity of the surface of the rock upon which the gravel lay, 
although three separate rows of slieet-piling tvere driven through 
it to the rock and well puddled between." Where sheet-piling 
could be so easily driven, an iron rod ought to have penetrated. 
The subsequent cost due to this error is not given ; but the 
following estimate will be below rather than above the actual 
cost, and will, I hope, have the effect of strongly impressing 
upon young engineers the importance of obtaining reliable in- 
formation, especially when it can be obtained at a cost of only 
$100 to $200 at the outside: 

1100 cu. yds. masonry @ $8= $8,800 00 

" " " " lifted from the pier, landed, cleaned, and 

piled, @ $3, 3>300 00 

rehandled and relaid @ $3, 3.3°° °° 

Constructing, pumping out of coffer-dam, and excavation, .... 5,000 00 

Constructing false-work, trusses, etc., to support the draw-span, . 5,000 00 
(Including in the above all material, labor, necessary plant, etc.) 

. Total cost, $25,400 co 

» 

The writer has made no estimates of actual quantities and 
costs, and hopes that he has not overestimated the costs. He 
hopes also that the engineer of this work will not consider the 
above as intended for a criticism of his skill or ability. We all 
make blunders, and the writer has recorded his own in several 
places in this volume ; and he has taken every occasion to 
describe failures and blunders, with no other object in view than 
that of recording faithfully all facts exactly as they have oc- 
curred, as he felt it his duty to do ; and he further believes that 
more useful knowledge and experience can be obtained from a 
study of blunders and failures than from successes. 

The writer had a somewhat similar experience when build- 
ing a bridge across the Warrior River in Alabama. He sounded 
with a solid-pointed rod, and reported rock at 5 ft. below the 
bed of the riv*er, covered with sand and gravel. This result 



$j6 SUPPLEMENT. 

was somewhat anticipated, as the rock upon which stood an 
adjacent pier ioo ft. from the one under examination waswell 
exposed at low-water. There were only some 6 or 8 ft. of water 
at lower stages at the site of the pier. He put in a coffer-dam, 
however, which developed the fact that there was at least 15 
ft. of sand over the rock ; and having pumped the water out 
and having excavated about 10 ft., it was then found necessary 
to drive piles in the bottom of the excavation to a further 
depth of 15 to 20 ft. in order to obtain a safe resistance. 

One of our most eminent Southern engineers constructed 
a bridge across the Big Sandy River, W. Va., on a bed of 
bowlders and gravel at no very great depth below the bed of 
the river, which stood for many years without showing any 
settling, but after more than ten years of constant use one of 
these piers settled out of line. The writer called upon him 
for advice as to the suitableness of a bed of clay, under the 
Ohio River at Point Pleasant, W. Va., for supporting a high 
and heavy pier with its superstructure and load. His reply 
was, that when younger he thought that he knew a good 
foundation bed when he saw it, but after the settling of the 
Big Sandy pier he had come to the conclusion that he knew 
but little of this subject. Long experience will generally make 
us more cautious, and therefore safer advisers. 

The engineer who has never blundered and never met with 
any failures has had but little experience or has acquired but 
little useful information, unless he is wise enough to profit by 
the experience of others, and has put himself to the trouble of 
acquainting himself with their failures. 

THE ACTUAL RESISTANCE OF BEARING-PILES. 

92. The importance of the subject of the bearing power of 
piles cannot be overestimated, and any information on the 
subject is valuable and instructive, and no excuse is needed 
for again referring to it. The following tables and remarks 
are taken from the columns of the -Ensrineerinsr Nezvs of Feb- 



SUPPLEMENT. 377 

ruary 23, 1893. Outside of the valuable statistics given, the 
object of the article seems to be to prove that the formula 

Safe Load = — ■ — , (I) 

s-{- 1 

in which w = weight of hammer in tons or pounds (the safe 
load being in the same unit) and h = its fall in feet, s = set 
under last blow in inches, will give safe and reliable working 
loads. On this point the editor says : 

" No formula can attempt to state exactly how much should 
be spent in such a case, or how much load can safely be placed 
on the pile. What the Engineering News formula does pur- 
port to do is to set a definite limit, high enough for all ordi- 
nary economic requirements, up to which there is no record of 
pile failures, excepting one or two dubious cases, where a hid- 
den stratum of bad material lay beneath the pile, and above 
which there are instances of both excess and failure, with an 
increasing proportion of failures as the limit is exceeded. 

" If it does this, as it is believed to do, it is in all cases a safe 
guide, having the risk of semi-fluid material existing beneath 
the foot of the pile, and in most cases a sufficient guide as well. 
But when a large number of piles are to be driven, or extra 
heavy loads are to be sustained, ordinary prudence would dic- 
tate the ascertaining by experiment just what the piles will 
bear, or, if failure would do no great harm, taking chances with 
greater loads without experiment, under favorable conditions. 
The formula is not intended to be rigidly applied to such 
cases as this." The above statement really contains all that the 
writer of this volume has contended for, when discussing the 
value of pile-driving formulae. 

The comparative merits of the Engineering News formula, 
Trautwine's formula, Crowell's modified formula, Sanders' 
formula, have been the subject of much discussion, heated and 
even acrimonious ; and as the writer has taken little part in the 
battle of the formulae, and is going to recommend the Engineer- 
ing Nezvs formula, if any is necessary or used, no comparisons 



378 S UPFLEMEN T. 

will be made, and the formulae results given below refer only 
to this latter formula in the following records. 
TABULATED RECORDS. 
Table I. 

Actual Safe Load by 

Locality and Soil. Hammer, Fall and Set. T & Eng. News 

Formula. 

Chestnut Street Bridge 1,200 lbs., 40 ft. 

Mud fin. 40,300 29,100 lbs. 

Neuilly Bridge 2,000 lbs., 5 ft. 

Gravel 0.016 in. 105,300 19,700 " 

HullDocks 1,500 lbs., 24 ft. 45,000 

Mud 2 in. to 56,000 24,000 " 

Royal Border Bridge 1,700 lbs., 16 ft. 

Sand and gravel 0.05 in. 156,800 53,700 " 

Phila. Experiments 1,600 lbs., 36 ft. 14,560 

Soft mud 18 in. to 20,120 6,060 " 

U. S. test-pile 810 lbs., 5 ft. 

Silt and clay 0.375 in. 59>6oo 6,600 *' 

French rule 1,344 lbs., 4 ft. 

No set. 56,000 10,742 " 

" The Engineering News formula gives the closest approxi- 
mation of the three ; and secondly, this formula for ultimate 
load (= six times the safe load) is not intended to be used for 
determining ultimate loads, and not alleged to give them with 
any accuracy, for the reason that the ultimate load is a much 
more variable quantity than the permanent safe load. At 
least we so understand it ; and certainly the safe load is the 
only thing we are aiming to determine or care to know." 

" It should be borne in mind that in some if not all of 
these cases the surrounding soil bears an unknown proportion 
of the load, so that the load actually coming on the piles may 
be several times less than stated." 

Table II. 

SUMMARY OF INSTANCES OF BEARING POWER OF PILES 
GIVEN IN MORE DETAIL BELOW. 

Case No. ActuaMJltimate Sa^Loadby Factor . of . Sa fety. Material. 

1 13,333 x > 68 4 7-9 Mud 

2 14,560 6,067 2.4 " 

3....... 22,400 23,450 — 1.0 " 

4 44,800 28,333 i-6 " 



SUPPLEMENT. 



379 



Case No. Actu ?> Ultimate 
Load. 

5 i I5 ' 175 I 

} to 47,375 I 

6 59,6i8 

7 75»ooo 

8 224,000 

9 13,440 

10 \ 6 "»°o + 

I to 13,300 + 

„ J 6,400 + 

"( to 13,333 + 
12....... over 22,400 + 



Safe Load by 
Formula. 



11,400 

6,74! 

44,080 

112,000 

8,020 

9,520 

10,183 

to 20,000 

10,667 

to 11,790 

37,500 



Factor-of-Safety. 
\ ^ 4-1 f 

8.8 

1.7 , 
2.0 

1-7 

1.4 
Not determinable. 



Material. 

Alluvial 

Mixed 
Sand 

Sandy 
Mud 



TESTS OF PILES IN WHICH THE RESISTANCE TO EXTRACTION 
IS THE ONLY EVIDENCE AS TO ULTIMATE BEARING POWER. 



Case No. 



Actual Ultimate 
Load. 



j 490 

13 ( to 1,288 

14 15,850 

I 25,000 

x 5 \ to 50,000 

[ 50,000 

J 6 ] to 83,000 

17 \ 7i,3oo 

J to 71,300 



Safe Load by 
Formula. 

108 

to 251 

25,067 
5,000 
5,000 

51,250 ) 
3,000 y 

12,800 

17,920 



Factor-of-Safety. 



to 



( 12,800 1 
( to 17,920 ) 



Material. 

Sandy 

Clay 

Unknown 

Rotten rock 
Sand 

Clay 



A detailed account of experiments for case No. 1 above 
has been given already. See Art. 42, par. 84. 

Case 2. Philadelphia, 1873. Soft river mud. Trial pile 
loaded with 14,560 lbs. five hours after driving, and sank but a 
very small fraction of an inch. Under 20,160 lbs. it sank f in.; 
under 33,600 lbs., sank 5 ft. (Records, Table I, show hammer 
weight 1600 lbs., falling 36 ft.; penetration or set 18 in. Safe 
load by formula, 6067 lbs.) 

Case 3. Mississippi River at East St. Louis, 1868-69. 
Soft muddy bottom, with 5 or 6 ft. of water. Piles in tempo- 
rary railway trestle of three-pile bent, 15 ft. from centre to 
centre, driven about 20 ft. Penetration, 2| to 3 in. The piles 
settled badly in a very short time under locomotives weighing 



3 80 SUPPLEMEN 7\ 

not over 30 tons, so that the load on a pile could hardly have 
exceeded 22,400 lbs. (Safe load by formula,— taking 27^ ft. 
mean fall, 2| ins. mean penetration, 1600 lbs. hammer,— 23,450 
lbs. Many of the data of this case are quite dubious, especially 
the weight given for locomotives. There were very few, if any, 
in Missouri in 1868-69 so light as 30 tons. It is more likely 
the load on each pile was double that stated.) 

Case 4. Perth Amboy, 1873. Pretty fair mud, 30 ft. deep. 
Four piles, 12, 14, 15, and 18 ins. diameter at top, 6 to 8 in. at 
foot, were driven in a square to depths of from 33 to 35 ft. 
Distance apart not given. A platform was built upon the 
heads of the piles and loaded with 179,200 lbs., say 44,800 lbs. 
per pile. After a few days the load was removed. The 18-in. 
pile had not moved ; the 12-in. pile had settled 3 in., and the 
14 and 15 in. piles had settled to a less extent. 

(Hammer 1700 lbs., falling 25 ft, with 2-in. penetration. 
Safe load by formula, 28,333 lbs -) 

Case 5. The record of driving uncertain and unintelligible. 

Case 6. Proctorsville, La. Material : mud, sand, and clay ; 
wet. Trial pile (driven alone) said to have been 30 ft. long, 
yet it is said to have sunk 5 ft. 4 in. by its own weight, and to 
have been driven 29 ft. 6 in. deeper, making 34 ft. 10 in. 
driven length ; cross-section I2|- X 12 ins. at top, and n£ X n 
ins. sharpened to 4 ins. square at foot. Weight, 161 1 lbs. Head 
capped. Pile bore 59,618 lbs. without settlement, but settled 
slowly under 62,500 lbs. Fall during last ten blows regulated 
to 5 ft. exactly. Penetration last ten blows ranged from ^ to 
\ in.; mean, 0.35 in.; last blow, f in. 

(Hammer, 910 lbs. ; safe load by formula, 6741 lbs., being 
very far below what the pile actually sustained. This is 
another case of those piles in soft material whose resistance is 
not fairly measured by the blows given when first driving, but 
can only be fairly gauged by trying blows after the mud has 
had time to set.) 

'Case 7. Buffalo. Material : wet sand and gravel. Piles 
driven in nests of from 9 to 13 piles. Test-pile of beech, 20 ft. 



SUPPLEMEN T. 3 8 1 

long after being driven and cut off. Driven length 20 ft., 3 ft. 
in stiff clay; cross-section, 15 ins. diameter at top. A load of 
50,000 lbs. remained on the pile for 27 hours, but produced no 
appreciable effect. The load was increased 20,000 lbs. at a 
time, and left for 24 hours after each increase. A gradual 
settlement, aggregating f in., took place under 75,000 lbs., and 
the pile then came to rest. The total settlement increased to 
\\ ins. under 100,000 lbs., and to 3^- ins. under 150,000 lbs. 
During the experiments the ground was kept in a tremor by 
the action of three pile-drivers at work on the foundations. 
Subsequent use shows that 74,000 lbs. is a safe load. 

(Hammer, 1900 lbs. ; fall, 29 ft.; set, 1.5 in. Safe load by 
formula, 44,080 lbs.) 

Case 8. As a result of the tests in Brooklyn, N. Y. Ma- 
terial : wet, loamy, micaceous quartz sand, becoming quicksand 
wherever it was much trodden. As the result of the tests it 
was believed that for a pile driven 33 ft. into the earth to the 
point of ultimate resistance, with a ram weighing 2240 lbs. 
and falling 30 ft. at the last blow, the extreme supporting 
power due to frictional surface was 224,000 lbs., or 1 ton per 
superficial foot of the area of its circumference. 

(Safe load by formula for 0.0 and 0.2 in. penetration, 
134,000 to 112,000 lbs.) 

Case 9. Material : sand, with some mud. Piles seem to 
have been driven either by a steam pile-driver delivering 60 
blows per minute, ram weighing 2205 lbs., falling 30 in., or 
by an ordinary hand engine, ram 992 lbs., fall 6 ft. 7 in. 
Penetration at last blow, § in. to \\ in. If the penetration 
was over f in. on the average of the last 100 blows, the rule 
was to put in extra piles. The load seems to have been about 
13,440 lbs. per pile. 

(Safe load by formula for 2205-lb. hammer, 8020 lbs. ; with 
the 992-lb. hammer, safe load 9520 lbs.) 

Case 10 belongs to the same set of experiments as Case 1, 
and is found fully described in part first of this volume. 

Case 11 also belongs to Case 1. Safe load by formula, 
10,667 to 11,790 lbs. 



382 SUPPLEMENT. 

Case 12. Lake Pontchartrain Trestle, La. About 6 miles 
of trestle crossed the lake proper, and the remainder (16 miles) 
crossed the adjoining sea-swamp. Four-pile bents 15 ft. be- 
tween centres. Material of swamp : several feet of soft, black 
vegetable mould, lying upon soft clay, with occasional strata 
of sand 1 to 2 ft. thick. Piles sank from 5 to 8 ft. of their own 
weight, and then about as much more with hammer (about 
2500 lbs.) resting on head of pile. Two piles 65 ft. long were 
driven, one on the top of the other, and penetrated 9 in. with 
over 100 ft. driven ; but a 30-foot fall, 30 minutes after driving 
a pile, gave only 3 in. penetration. Piles 65 to 75 ft. long ; 
weight of ram about 2500 lbs. ; fall about 30 ft. ; penetration 
3 to 12 in. " No settlement has been observed in the entire 
length of the structure to date." With four piles in a bent, 
and the bents 15 ft. centres, the load on each pile probably 
has not exceeded 22,400 lbs. 

(Safe loads for 3, 6, 9, and 12 ins. penetration, 37,500, 
21,430, 15,000, and 11,538 lbs. by formula. "As the only 
proper fall to be considered in a case like this is the 3-in. pene- 
tration, which occurred after 30 minutes' intermission, the 
check here is excellent.") 

The remaining cases in Table 2, viz., 13, 14, 15, 16, and 17, 
only are important as enabling inferences to be drawn as to 
the bearing power of piles from their resistances to being 
pulled out after being driven. In Cases 13 and 14 the piles 
were lifted by the action of ice, and the load was estimated by 
the uplifting force of ice, which was taken at 18,850 lbs. per 
pile. " The case, in fact, is one of exceptionable doubtfulness 
in all respects." 

Case 15. Material: wet, decomposed mica schist. A 
wrought-iron pipe, 3^ ins. outside diameter, 3 ins. inside, was 
inserted in a bore-hole 6 in. in diameter and 30 ft. deep, and 
driven 14 ft. to rock. After several hours' work with block 
and fall, the pipe was pulled in two by using two hydraulic 
jacks of unequal power, one on each side, by means of which 
the pipe had been raised 8 ins. The fracture took place in 



SUPPLEMENT. 383 

the thread, where the wall thickness was reduced from \ to \ 
in., leaving a cross-sectional wall area of 3^ X 3-i4!6 X \ = 
1.23 sq. ins. 

Since the pipe had been slightly raised under the pull 
which soon after caused its rupture, the latter was evidently 
about equal to the resistance of the pipe to being withdrawn. 
We can estimate at the amount of this pull by estimating the 
tensile strength of the iron at the point of rupture. 

The conditions of the experiment were very crude, but 
considering that the pipe was no doubt weakened by canting 
from side to side under the unequal forces exerted by the two 
jacks, as well as by repeated blows in driving and repeated 
tensile strains in drawing, and by the removal of the outer 
shell of the iron, in cutting the thread, the tensile strength- 
could hardly have exceeded 40,000 lbs. per square inch, and, 
on the other hand, it was perhaps not less than 20,000, giving 
25,000 to 50,000 lbs. as the extreme load. 

(Hammer of 350 lbs. falling 8 ft., set ■§■ in., sustained 25,000 
to 50,000 lbs. Safe load by formula, 5000 lbs. scant.) 

Case 16. Pensacola, Fla. Material: clean, hard, sharp, 
white quartz sand. All the sand would pass through a sieve 
having openings ^ in. square. Water filtered through it came 
out perfectly clear. One cubic foot of it would hold 6 qts. of 
water. The 2-ton hammers could only drive it about 20 ft. 
The water was about 1 1-| ft. deep. Seven piles, selected as 
representing the average of all, were tested with upward pulls 
of 20,000 lbs. each without moving, and one of these was after- 
wards tested with upward pulls sufficient to cause motion (as 
recorded below), and finally withdrawn. This pile was 29 ft. 
long, 16 ft. in sand, including its point — 2 ft. long. One foot 
of this length was in loose sand, which had been excavated 
and had fallen back. The average diameter of the part in the 
sand was 13J ins., including the bark. Weight of pile 1632 lbs. 
Pile tested two months after driving. As neither the weight 
nor fall of hammer nor set are given, the formula can only be 
applied by assuming the necessary data. 



384 SUPPLEMENT. 

Safe Load by Formula. 

1st W— 2,200 lbs., ^ = 30 ft., j = 0.5, 88,000 lbs. 

2d W = 4,100 " /* = 33 " j = 0.0, 270,000" 

3d .W =4,100 " h—xo" s — o.b, 51,250" 

The tests on the trial pile resulted as follows : 

78,000 lbs No movement. 

80,000 " Resisted \ min. and then rose very slowly. Rose 2\ 

ins. in 30 minutes. 

82,000 " if minutes. 

83,000 " \ minute. Rose 2 \ ins. in all in 30 minutes. 

60,000 " 18 hours. No movement. 

04,000 / Rose 3 ins. in one hour, 6 ins. in all. 

74,000 " J 

50,000 " For two days. No movement. 

The very small loads obtained by the tests in this case seem 
to confirm the view already expressed, that the resistance of a 
pile to an upward pull must be less than that to a downward 
pressure, especially in a pure sand, exerting relatively a small 
resistance to being broken up, but offering a great resistance to 
a downward pressure. 

Case 17. Albert Dock, Hull, England. Material: compact 
bluish clay, above which there were from 3 to 5 ft. of peat, and 
above this silt and sand in places. Piles of ordinary rough 
Memel bark timber, from 10 X 12 to 14 X 15 ins. ; average \2\ 
ins. square, from 20 to 40 ft. long. Driven length from 6 to 
30 ft. ; average \Z\ ft. Most of the piles were driven from 10 
to 20 ft. into the clay, and were nearly or quite in that material 
alone ; but a few of the shorter piles, driven in a sloping side 
of the dock, were entirely in the silt, while a few others entered 
the peat without reaching the clay. The piles were driven 
close together in two rows 5 ft. apart forming a coffer-dam, the 
space between the two rows having been filled with puddled 
clay to above high-water mark. Before the piles were with- 
drawn the puddle was removed down to a level rather under 
high-water mark of ordinary neap tides. Weight of ram 2240 
lbs., height of fall varied from 5 to 6 ft., and the penetration 
from 0.5 to 0.75 in. Four hundred and twenty piles were 
withdrawn and 300 observations recorded. The force was 
applied by men working a winch and estimated by testing that 



SUPPLEMENT. 385 

of the men in lifting known weights. The piles were drawn 
consecutively, so that one side of each pile was nearly or quite 
free from frictional contact, the opposite one was in loose con- 
tact with the adjoining pile, and only the remaining two sides 
resisted by friction with the ground. 

The average total force required to draw a pile was 75,869 
lbs. The author deducts from this 2340 lbs. ( = 12 X 12 in. 
X 15 lbs. per square inch) for suction and 2240 lbs. for weight 
of pile, leaving, say, 71,300 lbs. as the frictional resistance to 
drawing the pile. 

(Safe load by formula with f-in. set after 5-ft. fall, 12,800 
lbs.; with ^-in. set after 6-ft. fall, 17,920 lbs.) 

The writer regards the above records as the most complete 
and satisfactory of any heretofore published, and although 
there is a noticeable want of uniformity and consistency in 
many respects, much can be learned from a careful study of 
all of the facts. The methods of testing are suggestive, and 
the importance of accurate records are clearly set forth, and 
whereas there are great differences between the actual loads 
and the loads obtained by the formula, a comparison of these 
would seem to lead to the conclusion that what is claimed by 
the authors of the formula, viz., that the formulae will usually 
err on the safe side, can be reasonably admitted. 

As was mentioned in another place, it is but reasonable to 
suppose that it would require a smaller force to pull a pile than 
it would to cause it to sink ; as in the first case when the pile 
is lifted a gradually decreasing surface is in contact with the 
surrounding soil, and in fact in the stiffer soils it is only neces- 
sary to move the pile but a few feet upward before the fric- 
tional resistance will disappear almost entirely if the lifting force 
is accurately in the prolongation of the axis of the pile ; whereas 
in sinking a pile by direct pressure, gradually increasing 'sur- 
faces are presented in contact with the soil, so that not only 
has frictional resistance to be overcome, but a certain amount 
of lateral and downward compression of the material has to 
be effected by the required displacement of the material. 
This explains the fact that structures founded on piles often 



386 SUPPLEMENT 

settle a few inches, and then remain fixed for a time, when a 
small additional settlement may take place. 

PRESERVATION OF TIMBER — VULCANIZED TIMBER. 

93. The great importance of increasing the durability of 
timber, and of devising some means by which many kinds of 
timber which are now considered useless can be utilized, has 
been realized by a few engineers and builders, but has not 
received as much recognition as the subject demands. There- 
fore the writer wishes to give some prominence to a process 
which is not generally known, by which it is claimed all woods 
are increased in strength and stiffness, are made more dura- 
ble, and that many kinds of wood now considered worthless 
can be utilized in building any kind of timber structures. 
Several methods have been given in the preceding pages of 
preserving timber (see Article 38). It has not, I believe, been 
claimed that any of these methods increased the strength of 
timber, or even that to any extent it rendered the weaker and 
inferior grades suitable for the ordinary structures. 

The method now to be described seems to the writer to 
be rational, simple, and economical, and if the results thus far 
obtained are confirmed by future experiments, and the pro- 
cesses can be economically carried out, it would seem that the 
question of timber preservation will have been satisfactorily 
solved. An interesting description of the method of produc- 
ing so-called " vulcanized timber " will be found in the Electri- 
cal World, March 11, 1893. From this magazine the following 
points of interest are mainly taken. 

Wood as it occurs in nature consists of cellulose impreg- 
nated with resin, volatile oils, sugar, gum, tannin, protein 
bodies, and the usual mineral constituents of plants. When 
wood is heated, as in ordinary distillation, the cellulose decom- 
poses and a chemical change takes place between it and the 
natural constituents of the sap, resulting in a most powerful 
antiseptic mixture containing acetic acid, methyl alcohol,, 
acetone, methyl acetate, tarry matter containing phenol, 
creosote, carbolic acid, and about thirty other chemicals of 



SUPPLEMENT. 387 

lesser practical importance. These chemicals and antiseptics 
result from the action of heat on the natural sap of the wood, 
and are entirely different from the original sap, which allows 
the attacks of microscopic fungi and decay. If timber is 
heated to the temperature which will produce the above 
change and the antiseptic mixture is kept in it by pressure, 
instead of distilling it out, experiments show that the change 
will produce a stronger and more durable timber than it was 
originally. " Wood-vulcanizing is heating wood and timber 
under great pressure." The wood is heated in closed cylin- 
ders from eight to twelve hours, at a temperature ranging from 
300 to 500 Fahr., while under a pressure of 150 to 200 lbs. 
per square inch. A circulation of superheated and dried 
compressed air removes the surface moisture and any water 
that does not take part in the reaction, and combine with the 
woody constituents. Cylinders of steel 105 X 6£ ft. in length 
and diameter, respectively, are employed. The timbers to be 
treated can be loaded on cars or trucks and run direct into the 
cylinders. When subjected to the proper temperature and 
pressure during the necessary interval of time, the timber is 
removed. "This apparently makes decay impossible by seal- 
ing up the pores with antiseptic matter, which becomes solid 
on cooling. The changed sap is very dark or black." 

" The process of vulcanizing seasons all timber, preventing 
any further warping, checking, or cracking. Such timber is 
not influenced by atmospheric agencies, bacteria or spores, and 
requires no paint for protection. The albuminous constituents 
of the natural wood have been coagulated by the high heating, 
and rendered insoluble." 

These are seemingly extravagant claims, which should only 
be accepted when fully established by careful and accurate 
experiments in sufficient numbers and after a sufficient lapse 
of time — at least so far as durability is concerned. But when 
so established they should be accepted by engineers, whether 
in conflict with theories or not, and even when seeming to be 
unreasonable. Some chemists have stated to the writer that 
it seems probable that the chemical changes could take 
place only when such a temperature was reached that would 



388 SUPPLEMENT. 

char and destroy the woody fibre ; so theoretically the results 
seem doubtful. But they at least seem reasonable in view of 
the facts: 1st. That timber is seasoned artificially by being 
subjected to hot air for comparatively short periods of time. 
2d. That timber is rendered more durable and capable of re- 
sisting the attacks of the teredo when the moisture has been 
removed and the pores refilled with some at least of the 
above-mentioned antiseptic compounds by pressure. 3d. It 
would seem to be more economical to convert the fluids found 
in the timber into antiseptics and keep these in the timber by 
similar processes to those adopted when creosote is forced 
under pressure into the timber, the creosote being first ob- 
tained by distillation from other and different timber. 

However, to sustain the claims of the inventors or users of 
the vulcanized process for preserving timbers, they offer the 
following results of experiments and experience. And when 
we remember the fact that the annual consumption of timber 
in this country, equals twice the amount of material supplied 
by the annual growth of our forests, it is to be hoped that an 
efficient and economical means of preserving, strengthening, 
and hardening timber has been discovered. 

Experiments made on a number of specimens show that 
the strength is increased as much as 18.78 per cent, and 
amount of deflection is decreased by 13 per cent, as compared 
with specimens of the same timber that have not been treated. 

Timber not treated by the vulcanizing process, but painted, 
showed a loss of 38.12 per cent in strength as compared with 
the treated timber, after a lapse of some considerable time in 
exposed situations. Frames made partly of the vulcanized 
timber and partly of the timber in its natural state, after the 
lapse of eight years or more were found sound and solid so 
far as the prepared timber was concerned, but those parts 
formed of the natural timber had almost entirely rotted. Mr. 
Tracy, late Secretary of the Navy, made a thorough investiga- 
tion of the subject, and recommended that the vulcanized 
timber should be used in certain parts of the ships being con- 
structed for the Government. These facts would seem to 
justify, in part at least, the claims of the manufacturers. 



TENSILE STRENGTH OF CEMENTS. 389 



TENSILE STRENGTH OF CEMENTS. 

REQUIREMENTS. 

Tensile Strength required 
in Pounds per square inch. 
One day. One week. 

Portland cement, neat no 300 

" " 1 to 2 mortar 100 

Fineness: 80 per cent must pass through a sieve of 10,000 meshes. 
Average Tensile Strength in Pounds. 

f lme of set in water -j ^^ wee [j mon. year, years, years, years. 

Portland, Burham (neat) 167 429 615 798 700 764 782 

" 1 to 2 mortar 141 258 468 532 632 658 

" 1 to 3 " 169 224 404 520 552 

Giant (neat) 140 348 422 682 694 736 771 

" 1 to 2 mortar 166 280 490 564 680 674 

1 to 3 " 140 234 420 512 572 

Rosendale, Union (neat) 100 240 228 510 542 650 654 

" 1 to 2 mortar 34 94 394 43° 514 522 

A natural Portland cement from Maria Island, Tasmania, weighs 113 lbs. per 
bushel. Specific gravity 3.152; slow setting. 

7 days. 14 days. 28 days. 

Tensile strength (neat) 536 536 646 

" " 1 to 3 mortar 150 ... 258 

The above is taken from Eng. News, April 13, 1893. It 
is of special interest, as the tables contain the longest time tests 
of which we have any records, and, extending through a period 
of four years, give the gradual increase in hardness and strength 
with increase of age. The fall in strength between the one- 
and two-year test of the Burham neat cement is due either to 
a typographical error or an error in the second ; the one-year 
test should no doubt be 698 lbs. The results are, however, 
recorded as found in the columns of the News. There is also 
apparently an error in the one-week test of same cement in the 
1 and 2 or the 1 and 3 mortar. 

These tables are given, as interesting and instructive results 
of experiments, without comment. 



INDEX. 



Abutments: 

arches in Art. IO » Par - Io8 ; Art. x 4> Par - *3% 

for arches - " 2 4, " 25610265 

form of, wing, U, and T " 10, " 105; Art. n, Par. 114 

designing of Art. 10, Par. 106 

Arches: 

abutments for *4» x 38 

■ « " Art. 24, Par. 256 to 265 

apron walls and paving • •• ■ Art. 12, Par. 128 

brick, used in I0 > *59 

" construction of Art. 16, Par. 160, 161, 162 

centresfor " 17, " 185,186 

construction of Art. 12, Par. 120; Art. 17, Par. 185 

culverts Art. 24, Par. 251, 252, 253 

definition of terms used in " 12, " 123,124,125 

development of soffit " 13, " 132, 133, *34 

direction of pressure in Art. 12, Par. 119 

hoop iron in I0 > 163 

lengthof " I2 > " t26 

line and centre of pressure in " 12, 116 

masonry of Art. 12, Par. 118, 127, 129, 130 

resultant pressures Art. 12, Par. 116 

rolling loads on J 4> x 36 

rupture, joint of I2 , 116, 117 

rules in construction of 12, 122 

stabilityof " l6 > " l6 7 

" ■., " 14, " 136,137 

stone better than brick " 16, 168 

theoryof " ™> " "5 

<« " 17, " 170-184 

skew " 13, " 131 

thickness of keystone T 4. !35 

tunnel » " * 6 > "164,165 

uses of I2 » I21 

u a " 16, " 166 

391 



392 



INDEX. 



Bearing resistances of materials: 
clay 



Art. 



clay and sand. 



conclusions Art. I, Par. 14, 1 5 ; " 

determination of.. Art. i.Par. 18; Art. 42, Par. 84, 85; " 
gravel Art. 1, Par. ir, 14; " 

of piles Art. 57, Par. 77 



sand. 



silt. 



tables of 

" " Art. 28, Par. 306; 

tests should be made 

Brick: 

arches — see Arches. 

bad, use of Art. 

compressed " 

durability of " 

making " 

manner of building Art. 15, Par. 

piers Art. 15, Par. 148 

sewer, pavements " 15, " 157,158 

strength of Art. 15, Par. 147, 152, 153 

walls of " 15, " 139,142,143 

" pressures on Art. 15, Par. 151 



1, Par. 


10 


57, " 


76, 77 


1, " 


13 


57, " 


76 


56, " 


80 


57, " 


76 


29, " 


4 


57, " 


76 


also see 


Appendix 


42, Par. 


84, 85, 86 


1, " 


11 


50, " 


25. 29 


57. " 


76, 77 


1, " 


12 


50, "' 


46 


57, " 


76 


1, " 


16, 17 


56, " 


76 


1, " 


18 


t. 15, Par. 150 


15, ' 


155 


15, " 


149 


15, ' 


140, 141 


143, 144, 145, 146 



" thickness of 

" how measured 

when to be used 

Bridges described: 
Cairo — 

construction, method of sinking and depths reached. 

number and length of spans 

East River 



15, 
16, 

15, 



156 
169 
154 



Art. 50, Par. 29 



Hawkesbury. 

Memphis 

Morgan City. 



50 : 
50, 

54 
43 
54 
50: 
54 
43 



29 
24, 25 

65 
6 

65 
27 

65 
9 



INDEX. 393 

Bridges described: 

Parkersburg Art. 29, Par. 4 

Poughkeepsie ' 48. 5 

" 54, " 65 

St. Louis " 50, " 26 

«< " " 54. " 65 

Susquehanna and Schuylkill— 

timber caissons, construction of Art. 50, Par. 2g£, 30, 31, 32 

cribs on caissons., " 5°, " 30, 36. 37, 38 

coffer-dams Art. 50, Par. 31, 38; Art. 51, Par. 45 

Drawings Plates XIII, XIV, XV, XVI, XVII 

Caissons, launching Art. 50, Par. 33 

advantages in design 5°. ' 34 

accidents 5°. 35 

sinking, method of Art. 51, Par. 39, 40, 41, 42 

excavation below cutting edge Art. 51, Par. 43 

number and length of spans " 27, ; 279 

" " • " 54, " 65 

Tombigbee River " 5 1 , " 4« 

accidents 5 1 , ' 4° 

Point Pleasant Art. 27, Par. 286, 287, 288 

Caissons: 

pneumatic, defined Art. 48, Par. 1 

airin " 49, " ". I2 

air-lock " 49, " *3, *5 

<< " " 50, " 26,29 

air in, effects of Art. 49, Par. 18, 19, 20 

" " " " Art. 50, Par. 29 

air in, reducing ' 49, 22 

" " " " 5i, " 42 

combined with open crib Art. 52, Par. 48, 49, 50, 51, 52 

concrete in. Art. 51, Par. 44 

. construction of Art. 50, Par. 24, 25, 26, 27 

" " " 50, " 28,29,29^,32 

depths, limit of Art. 48, Par. 3; Art. 49, Par. 20 

excavating below cutting edge " 5 1 , ' ' 43 

for masonry abutments. .* 5 1 , '45 

iron used 5°, 2 8 

machinery for '49, 2 3 

pumps for mud 5 1 , ' 4 1 

sinking, method of ' 49> "16 

" " " Art. 50, Par. 39, 40, 41, 42 

shafts, pipes, valves Art. 49, Par. 13, 14, 17 

signals Art. 49, Par. 21 

with open crib • 5°, ' 3° 

Remarks " 5 2 , " 53 



394 



INDEX. 



" I9> 


' 196 


" 20, 


' 207 


" *9> 


' 198 


" J 9- 


' 197 


" T 9> 


' 196 


" 20, 


' 210 



Caissons, open: 

construction of Art. 31, Par. 20, 21, 22 

in bed of streams Art. 31, Par. 21; Art. 46, Par. 118, 119, 120 

" piles Art. 31, Par, 21 

" " Art. 46, Par. 118, 119, 120 

when used Art. 31, Par. 22 

Caisson and open crib combined: 

construction and design of , . . Art. 52, Par, 48, 49 

sinking, method of " 52, " 50,51,52 

uses of Art. 48, Par. 8; Art. 52, Par. 50, 51, 52 

Remarks Art. 52, Par. 53 

Cement : 

hydraulic, defined ...... 

brands of . . . 

effect of temperature on 

heavy slow setting 

light quick " 

Portland 

set of Art. 19, Par. 196, 199 

stones " 20, " 205,206,216 

testing Art. 19, Par. 196, 201; Art. 20, Par. 208, 209, 210, 211, 212 

weight of Art. 19, Par. 197; Art. 20, Par. 215 

Coffer-dams: 

clay puddle for Art. 30, Par. 15 

of earth " 29, " 6 

excavation in Art. 30, Par. 12, 13, 14 

expenses of, uncertain Art. 30, Par. 16 

masonry built in : " 30, " 18 

pumping out " 30, " II 

piles driven inside -, " 30, " 17 

timber, ordinary construction of " 30, " 7,8 

" single walls, " " " 30, " 9 

timber, on caissons " 50, " 31,32 

" " " construction of " 31, " 20 

with inside cribs " 30, " 13,14 

when used " 30, " 19 

Concrete, 

broken stone and gravel in " 2, " 24, 25 

composition of " 2, " 22 

crushing strength of " 3, " 38 

exact proportions " 2, " 33 

general rules in making " 2, " 31 

kind of stone used Art. 2, Par. 27, 29, 30 

mixing " 2, " 23,26,27,28 

proportions in Art. 2, Par. 24, 26, 27, 28, 32; Art. 50, Par. 29 

spread of base by Art. 3, Par. 34; Art. 57, Par. 76 



26, 


• 276, 


277 


25, 


' 272, 


277 


25, 


« 268, 


270 


27, 


' 286, 


287 


27, 


' 284, 


285 



index. 395 

Concrete: 

under Washington Monument Art. 2, Par. 31^- 

uses of " 3, " 34,35 

" " under water 

cu. yds. per barrel of cement 2, " 32 

Cost of work: 

brick, stone, concrete, earth Art. 25, Par. 267, 270; Art. 26, Par. 278 

caissons Art. 25, Par. 269, 270 

quarrying 

stone cutting 

trestles 

Ohio River Bridge 

Schuylkill River Bridge 

Susquehanna River Bridge Art. 27, Par. 281, 282, 283 

by contractors ••• " 25, " 273,274 

tables of cost and quantities. Art. 26, Par. 275, 278; Art. 27, Par. 279, 280-88 

remarks on Art. 25, Par. 266 

Cribs, ordinary: 

construction of Art. 29, Par. 3, 4 

sinking, method of " 29, ' 3,4,5 

sunk on rock " 29, 5 

filling broken stone with grout " 48, " 5 

Cribs for deep foundations: 

combined with pneumatic caisson Art. 52, Par. 48, 49, 50, 51, 52 

construction of Art. 48, Par. 2 

defined ■=•• " 48, 1 

designs for 48, 4 

" " of timber " 48, " 5 

" "of iron Art. 48, Par. 6; Art. 50, Par. 28 

" "on caissons Art. 50, Par. 29 

sinking, method of • 

sinking, difficulties of 

when used 

examples of — 

for Cairo Bridge 

" Hawkesbury Bridge 

" Poughkeepsie " 

" Susquehanna " Art. 50, Par. 30, 31, 32. 

" Schuylkill " " 50, 

Lighthouse, Diamond Shoal Art. 50, Par. 2S 

Remarks ■ 5 2 > 53 

Culvert: 

box and arch Art. 18, Par. 187, 188, 189; Art. 24, Par. 251, 252, 253 

waterway in Art. 23, Par. 245, 246, 247, 248 

pipe " 23, " 249,250 





" 48, 




3 




' 48, 


" 


7 




" 48, 


" 


3 




" 50, 


it 


29 




" 48, 


11 


6 




" 48, 


" 


5 


33 


34, 36, 


37 


38 


" 


3°, 36, 


37 


38 



396 INDEX. 

Cutting and dressing stones: 

chisel draft .'-. Art. 6, Par. 62 to 67 

gauging stones - • Art. 6, Par. 67 

method of <• " 6, " 64 

pitch line " 6, " 66 

requirements " 6, ' 65 

shapes, required " 6, ' 62 

tools used Art. 6, Par. 62, 63 

Cylinders: 

cushing, piers with piles " 32, " 23,24 

piers, without piles Art. 32, " 24 

of brick and concrete. Art. 56, Par. 75; Art. 57, Par. 80-85; also see Appendix 

of iron Art. 48, Par. 9; Art. 50, Par. 29 

Definition of terms Art. 28, Par. 289, 290, 291, 292 

Derricks " 28 " 293 

Formulae : 

for foundation projections Art. 57, Par. 76 

" beams and stringers " 4 r > " 7°, 7*. 72 

" joints and fastenings " 40, " 60 

" long timber struts " 41, " 68,73 

" driving piles " 42, " 91 

" " " " * " 43, " 92,93 

" building on soft soils " 47, " T 35 

" for wind pressure " 9, " 94 

" retaining-walls Art. 11, Par. 109, no, in 

' ' depth of keystones of arches. Art. 14, Par. 135 

" abutments of arches Art. 24, Par. 256, 257, 258 

" " " " " 24, " 259,260-265 

Foundation-beds : 

classification Art. 1, Par. 1 to 19 

conclusions I, 14, x 5 

failure of ' * I, "19 

general principles of Art. 1, Par. I, 2, 3, 4, 5, ,6, 7, 8 

pressure on " I, "10,11,12,13 

Tables of Art. 1, Par. 16, 17 

tests of " ii 18 

Foundations, construction of : 
by concrete — see Concrete. 
" caissons or cribs — see Caissons and Cribs. 

' ' timber, ordinary Art. 29, Par. 2 

"cribs " " 29, " 3 

" " " sinking " 29, " 3,4,5 

in coffer-dams " 30, " l8 

by " « — see Coffer-dams. 

masonry — see Masonry ; also " 3, " 36, 37 

inquicksand " 56, " 70-75 



INDEX. 



397 



Foundations, construction of: 

for high buildings. 

' ' trestles — see Trestles ; also 

" freezing process 

" injecting cement into sand Art. 48, 

definition of ». 

settlement of 

of masonry .... 

" steel and concrete 

" timber" " 

remarks 

by the Harris process 

Grout : 

defined 

in gravel and sand under water 



Art. 57, Par. 76, 79-87 

" 41. " 65 

" 55, " 67, 68, 69 
Par. 5; Art. 56, Par. 73 
Art. 2, Par. 20 



masonry. 



Ice : 

pressure and strength of Art. 9, Par. 94, 95; 

Iron bolts : 

strength of 

Joints and fastenings : 

in carpentry Art. 40, 

" 40, 

in masonry , 

principles of , 

relations between 

Lighthouse : 

iron crib 

Lime, quick 



" 29, 


" 2 


" 57, 


* 76 


" 57, 


' 76 


" 57, 


* 76 


" 2, 


' 21 


" 55, 


* 73 


" 7, 


' 82 


" 48, 


* 5 


" 56, 


' 73 


" 7, 


' 82 


" 22, 


" 229-244 


" 40, 


« 60 



Par. 53 

" 57 



54, 55- 56 

59, 60, 61, 62 
Art. 7, Par. 80 
40, " 64 
40, ' ' 60 

50, " 28 

19, " 200 

20, " 203 



Location of piers : 

base-lines 

steel tapes and base bars for 

steel wire 

triangulation for 

of bridges Art. 54, Par. 61, 62, 63, 64 

Masonry : 

ashlar 

backing or filling in 



54. 
54, 
54, 
54, 



Art. 7, Par. 78, 79 



batter on 

block-in-course. 

bond in 

classification of. 
dry stone 



7, 


sy 
' 79, 81- 


7, 


" 86 


7, 


' 77 


7, 


' 74, 78 


7, 


' 68 


7, 


' 72 



39» 



INDEX. 



Masonry : 

brick 

expansion of 

facing stones in Art. 5, Par. 60; 

footing-courses 

granite 

grout in 

header and stretcher — see Definition of Terms. 

inspection of 

joints in 

laying 

limestone 

neat line in 

rubble, rough 

" coursed 

" limestone 

' ' sandstone 

sandstone 

Masonry : 

appearance on the face 



Art. 3, Par. 34, 36 



coping 

piers, form of 

" stability of 

" pressures on 

" " " of ice and drift 

of retaining-vvalls 

starlings or cutwaters 

string-courses in 

principles and rules of construction 

Mortar : 

crushing and tensile strength Art. 19, Par. 201; 

cement, mixed with lime 

' ' hardening 

" proportions 

defined 

freezing of Art. 20, 

lime, proportions 

•' hardening 

pointing 

quantity in masonry 



salt in 

sand in 

yield per barrel. 

water in 

under water. . . . 



" 5, ' 


59 


" 6, ' 


65,67 


" 7, ' 


86 


" 7, ' 


69 


" 7. ' 


82 


" 5, * 


' 61 


" 7, ' 


' 80 


" 7, ' 


81, 85, 89 


" 7, * 


' 70 


" 7. ' 


86 


" 7, ' 


73 


" 7, ' 


* 74, 75, 76 


" 4, ' 


47, 48 


" 4. ' 


414-46 


" 7, ' 


' 7i 


" 7, ' 


87, 88, 89 


" 8, ' 


' 90 


" 7, ' 


88 


" 8, ' 


' 90-93 


" 22, ' 


' 229 


" 22, ' 


230-244 


" 22, ' 


233-244 


"IO, ' 


103, 104 


" 8, ' 


92, 93 


" 7, ' 


88 


" 18, ' 


190-195 


Art. 20, F 


'ar. 2ii, 212 


Art. 20, F 


ar. 202 


" 20, 


" 213, 214 


" 20, 


" 212 


" 20, 


" 202 


Par. 222, : 


J23, 224, 225 


Art. 20, F 


'ar. 204 


" 20, 


" 213 


" 20, 


" 226 


" 19, 


" 200 


" 20, 


" 202 


" 20, 


" 225 


" 21, 


" 227, 228 


" I 9, 


" 200 


" *9, 


" 200 


" 20, 


" 217, 2r8 



INDEX. 399 

Piers : 

all iron Art. 53, Par. 54-58 

" " screw-piles L - " J3 > <« gg 

" " " " construction of *' 53, " 56,57 

depth sunk " ^, " 57 

sinking by turning. .. . '. " 53, " 58 

" water-jet Art. 53, Par. 58; also see Appendix 

location of Art. 54, Par. 59 

cushing cylinder " 32, " 23,24 

" " construction of " 32, " 23 

" stability of. ..Art. 22, Par. 229-244; " 32, " 23,24 

masonry " 8, " 88-93 

pressures on " 9, " 94,95 

" stability of " g, " 95 

" dimensions of " 9, " 96 

" " " 27, " 279,288 

timber " 34, " 28 

" construction of " 34, " 28,29 

Piles : 

alignment in driving " 46, " 121, 122 

cutting off below water by divers *' 46, " 115 

" " " " machinery " 46, " 116,117 

driving piles, power used Art. 43, Par. 94, 95, 96, 97 

driving, record of Art. 45, Par. 108 

" in quicksand " 42, " 89 

determining bearing power " 42, " 84 

" " 43, " 93 

bearing power to be determined by experience and 

experiment " 42, " 90,91 

formula? for driving " 43, " 92 

" " " latest " 43, " 92 

discussion of formulae " 43, " 92,93,93^ 

holding piles in position " 46, " 124 

frictional resistance and direct support, dependent 

on " 43, " 92.93.g3i 

bearing power, examples of " 42, " 84-87 

" " Art. 57, Par. 77 ; also see Appendix 

frictional resistance of Art. 42, Par. 84, 85, 86 

" " 57, *' 79 

injury to, in driving Art. 42, Par. 81, 82, 87; " 57, " 77 

iron shoes for " 42, " 80 

for coffer-dams " 30, " 7,8 

inside of coffer-dams " 30, " 17 

knowledge of strata important Art. 42, Par. 88; also see Appendix 

preparing, for driving Art. 42, Par. 79 

pointing piles " 42, " 79 



44. 


" IOO 


46, 


" 123 


44. 


" 104 


44. 


" 104 


44, 


" 104 


44, 


" 104 


45, 


" 107 


44, 


" 102, 103 


3i, 


" 21 


34, 


" 28, 29 


42, 


" 83 



400 INDEX. 

Piles : 

purposes of driving Art 44, Par. 99, 101-104 

driving in rock beds. Art. 44, Par. 105, 106 

sinking by water-jet Art. 43, Par. 98; see also Appendix 

" " hand Art. 43, Par. 92, 96 

sand 

setting piles in the leads 

for trestles 

" " description and construction 

three and four pile-bents 

relative cost of construction 

temporary trestles 

for wharves, dikes, and jetties 

under open caissons 

' ' timber piers 

unreliability of formulae 

Pozzuolana Art. 20, Par. 219, 220, 221 

Pumps : 

mud and sand Art. 50, Par. 29; Art. 51, Par. 41 

force and centrifugal " 30, " 11 

Quicksand : 

defined ... " 56, " 70,71 

foundations in Art. 55, Par. 66, 67, 68, 69 

" " Art. 56, Par. 70, 72-75 

against walls " 11, " 113 

Quarrying : 

general principles 

blasting in 

drilling holes by hand 

" " " machinery 

explosives 

economy in 

Resistances : 

frictional 

" determination of 

on piles Art. 43, Par. 92,93,93!; 

Retaining-walls : 

as reservoir walls or dams 

formulae for thickness of 

frictional stability 

masonry in 

pressure of earth against 

stability against overturning 

theory of 

thickness of 

surcharged 



5, 


" 53 




5, 


" 54 




5, 


" 55 




5, 


" 56 




5, 


" 57 




5, 


" 59, 


60, 61 


57, 


" 77, 


78, 79 


57, 


" 78 




57, 


" 79 




Hj 


" in 




11, 


" 109- 


in 


10, 


" 107, 


108 


10, 


" 103, 


104 


10, 


" 97, 


98, 99 


10, 


" IOO 




11, 


" 109 




10, 


" 102 




24, 


" 259, 


260 



INDEX. 401 

Retaining-walls : 

surcharged. Art. 11, Par. 112 

to support quicksand or mud " 11, " 113 

Sand : 

uses of " 21, "227,228 

proportions of " 21, " 227, 228 

size of grain , " 21, "227,228 

qualities of good " 21, "227,228 

Soundings and borings, method, purposes, and impor- 
tance of Art. 33, Par. 25, 26, 27; also see Appendix 

Stones : 

for building, classified Art. 4, Par. 39, 40 

granite ,.. " 4, " 41 

limestone. " 4, " 47,48 

sandstone " 4, " 41-0— 45 

" examination of " 4, " 42,43,44 

two grades of " 4, " 46 

" strength of " 4, " 46 

absorption of water by " 4, " 50 

expansion of, with heat " 4, " 50 

tests of strength " 27, " 287 

Stress and strains : 

in timber " 41, " 67-74 

in iron , " 40, " 60 

Swamps : 

earth embankments on " 47, " 125-129 

crust of, not to be broken " 47, " 135 

building on " 47, " 135 

" "formulafor " 47, "135 

embankments, ordinary " 47, "130 

costof " 44, "133 

Tables : 

of long spans and depth sunk of some large bridges. " 54, " 65 

of timber, strength of " 41, " 72 

of stones and earth, strength of " 1, " 16,17 

mortar, strength of " 19, " 201 

cost of work, and quantities " 26, " 275, 278 

" " quarrying " 26, " 276 

" " Susquehanna River Bridge " 27, " 279-283 

" "Schuylkill " " " 27, "284,285 

" " Ohio River Bridge " 27, "286,287 

stones, resistance to crushing " 28, " 294-297 

" " cross-breaking Art. 28, Par. 294, 295, 298, 299 

tensile strength of mortar Art. 28, Par. 300 

adhesive " " " " 28, " 301 

absorptive power " 28, " 302 



402 INDEX. 

Tables : 

expansion and contraction Art. 28, Par. 303 

specific gravity 

angles of repose 

bearing power of soils. 

Timber 

description of 

general properties 

life of 

examination for rot 

preservation of Art. 38, Par. 43, 44, 45 

durability of Art. 38, Par. 47 

" " constantly wet 



protecting joints in. 
strength of 



strains in 

table of strength 

Trestles : 

framed, of timber 

types and construction of. 



spans over 15 ft 

timber used in 

joints in. 

braces 

under trussed stringers , 

over " " 

built beams for " 

foundation-beds for 

stresses in members 

strength of " 

determining dimensions 

bill of materials for 

comparative cost of pile and framed 

economical span in Art. 45, Par. 

terms of payment for.... Art. 46, Par. 113 

hints on designing " 46, " 114 

Wind, pressure of " 9, " 94,95 



28, 


" 


304 


28, 


<« 


305 


28, 


" 


306 


29. 


it 


I 


36, 


CI 


35-39 


36, 


• c 


40 


37, 


tt 


41, 42 


37. 


" 


42 


see 


alsc 


» Appendix 


38, 


Par 


• 47 


38, 


K 


48 


38, 


a 


49 


40, 


1 « 


63 


4i, 


ti 


72, 73 


4i, 


1 < 


67-71 


4i, 


(< 


72 


41, 


<< 


72 


35, 


it 


30, 31, 32 


35, 


tt 


30, 31, 32 


39, 


it 


50, 51 


4i, 


tt 


66 


35, 


(C 


33, 34 


35, 


" 


34 


40, 


<< 


53-62 


40, 


" 


58 


35, 


" 


33 


40, 


" 


64 


40, 


tt 


64 


41, 


" 


65 


41, 


" 


67 


4i, 


" 


68, 69 


4i. 


I i 


68, 69, 70 


41, 


tt 


74 


45, 


" 


109 


Par 


. IIO, III, 112 



"E I. 

ige, Point Pleasant, W. Va. 



r" High « :iwr 



Fig. 2. 



-is-H^i'd. 




mm 



END VIEW. 



PLAN AN 



D HORIZONTAL SECTIONS. 



Plate I, 
Pier No. 5, Ohio River Bridgb, Point Pleasant, W. Va. 

1 ' : 1 i 1 m — :* j— -f- 



HighJVaterjg 




low Water Pj-O 



Fig. 2. 




V»-»6J«™»-,".y. S | DE V | EW . 



END VIEW. 



PLAN AND HORIZONTAL SECTPOM3. 







Sacking. Fig. 2. Triangut a r-end Rubble Backing 



Plate II. 
Ends Large Stone. Fig. i. 



Circular Backing. 





Pointed-end Concrete Backing. Fig. 2. Triangui ar-end Rubble Backing. 



Plate III. 
Open Caisson or Crib, Ohio River Bridge, Point Pleasant, W. Va. 

•Fig. 2. 





Plate III. 
Coffer-dam with Inner Open Caisson or Crib, Ohio River Bridge, Point Pleasant, W. V.a 

Fig, i, _Fig. 2, 

n 



fciiiiiffiiB 



imp; 

I ■•■:." 



Sdurated'Claj- 

LONGITUDINAL SECTION 




Mmmm 




>:l 





a 


s 


*a 


12'i 12 


- j' 0" 


. l' 0"' 



7 

-■4 




Fig. 4. 

VIEW OF INNER CAISSON 



Plate IV. 
„, Fig. 4. 



CUSM.NG CYLINDER PIERS 



Fig. 10. 




/ 



Plate IV. 
,m ,-„ Fig. 4. 

^0.0-^f— 0.0— *< 



Pump Sounding .Apparatua 

Fig. ro. 

2i 




Plate V. 




Plate V. 




Plate Va. 
k on Tot of Pier and raised with it. 




123 

ENDVMEW 



Plate Va. 
Derrick on Top of Pier and raised with it. 



OliQ PLAN 




Plate VL 



PILE TRESTLES. 

50 &g sy ^ te xiexu djgr W T 12xl8x ^iirlFMr„_ 12)Cl! '-?i i^'..^y y 

Fig. 5. K\H eOsFig. 6. \J W Fig. 7. \\ I I A A Fig. 6. 




If"? 

[ bent. piles vertical outside piles inclined. * 3 pile bent. 3 pile bent. outside piles inclined. 

Fig. 2. Fig. 9. 



^^^^^#i^^^^^ 




g_v ,-t_fli q 



GENERAL PLAN OF DECK. 



ordinary framed trestle 
Fig. 4. « 



PILE TRESTLES. 




Fig. 1. , B timber pier. Fla j 

.„!. ..P^*] fc-e'-O'^ 4 PILE DENT - PILES VERTICAL OUTSIDE PILES INCLINED. " 3 PILE BENT. 8 PILE BENT. OUTSIDE PILES INCLINED. 




GENERAL PLAN OF DECK. 



Side Elevations. 




vrnmgjrijffttnB* 
Strut-bracing under Stringers. 



Fig. 3. 



J- 7x8x1.0 



L 25 -°~7, 



— 4 



; 2," 



PLAN OF DECK 

..■ I^± n „ h M 

-a.X-15=&J( . 




™u — 



Side Elevations, 




^m^t smri=$ 



End Elevation. 



Strut-bracing under Stringers. 



Plate VIII. 



\ils of Joints, Built Beams, etc. 



Fig. 5. 



Fig. 6. 



J. 4. 

APPED INCLINED POST INCLINED POST 



Fig. 7. 

TRUSSED beam 




Plate VIII. 
Details of Joints, Built Beams, etc. 



Fig.1. Eig.2. ,ElQ.3 

TENON „ DOVE TA 



FlO. 4. 



FlG. 5.. 



Fia. 6. 



FlO. 7. 

TRUSSED EEAM 




Fig.1. Fig. 2. Fig. 3. Fig. 4. 



Fig. 10. Fig.U. 




SOLID BEAMS 
Fig. 1. Elevation. Fiu. a. Plan 
Bolt & Keys, for Trestle Spans, 
from 12 to 15 feet. 
7 TIMBER BUILT BEAMS. 

Fig. 5a. 



Fig. la. 
Fl<j.-4a. Elevation— Bolt 4 Keys. 
Fl&..5a. End View for Spans-15 to 20 ft 




Plate IX. 
indoah Valley Railway. W. W. Coe, Chief Engineer. 




Plate IX. 
Four-story Trestle-bent, Shenandoah Valley Railway. W. W. Coe, Chief Engineer. 

r> n 



OxSxlO' 




'jaws ^=^m^=^% 

A ^ , ^H //T 5 12X9 \\ TpixU^ 



# „ „ , 

7J7X12X9 



^ txl 



FootofT.Struts ~t- Straining ; g: \ 
-, ™ Betim vX \ <i 






-2-X-15-X-1S 



Si^Hl 



-r - ' 




Bolstex 

and 
Packing Blocks ^ 



C5 



■T- 



rr"rn 



ax-is-x*- 



2* 



Top. View oi Stringers 



Fig. 2. 



ZGX3ZX3C 



Side view 



&X16 



=63EES3I=l. 




Plate X. 
Shoals Lighthouse. Designed by Anderson and Barr. 
Fig. i. 




gP^^^^I 




-27-raJius- — — -■ -^2:S"ra<hus — 

Fig. a. 
Fig. i.— Vertical Section. 
Fig. 2. — Horizontal Sections. 



Plate X. 

Caisson fob Diamond Shoals Lighthouse. Designed bv Anderson and Barr. 

Fig. i. 




Fig. i. —Vertical Section. 
Fig. 2. — Horizontal Sections. 



Plate XI. 
mbined Crib and Pneumatic Caisson. 



Fig. 1 




yf. M. PATTON, 

INVENTOR. 



Vertical Longitudinal Section. 
Iokizontal Sections at Several Points. 



Plate XI. 
Combined Ckib and Pneumatic Caisson. 

Fig. n 
D 




Pig. i Vhrtical Longitudinal Section. 

Fig. 2.— HoKizuNTAL Sections at Several Points. 



Plate XII. 
jbinkd Crib and Pneumatic Caisson. 



Tig. 4- 




ertical Section, Piles Driven in Interior, 
srtical Section, Sunk below Pneumatic Limit. 



Platk XII. 
Combinkd Crib and Pneumatic Caisson. 




Tig. 4- 



'■•:• 




'-.■•:-i-r^-(l- i r^3 



-• • - 



Fie. 3.— Part V»rvh.m. Sci : ' iven in Intfrior. 

FlG. 4.— Part Virtical Siction, Sunk bilow Pneumatic Limit. 



Plate XIII. 

rib and Coffer-dam, Susquehanna River Bridge, B. & O. Ry. 
Fig. I. 

SIDE VIEW 

B. 

77' 7H" , 




king Caisson 156,183,07 cub.ft. 

avation below cutting edge 3,405,24 » 



PLAN OF COFFER-DAM AND SYSTEM OF BRACING' 

Fig. 4. 



Plate XIII. 
Pneumatic Caisson, Crib and Coffer-dam, Susquehanna River Bridge, B. & O. Ry. 



Pig, 2. 

END VIEW 

- „ „ A. 
■V? . 311 1'' 

6 ft a, I 




ion 310,689,50 Fi.B.M 

" Crib 143,993,14 » 

U Coller-Dam 108,511,61 " 



Fig. 3. 

PLANS 
C. 
PLAN Or CRIB 





ii 


„JI 


ll 






:-------.- 




Ii d 


n— L 

_JLj 

fl 


=== 






II 
jj 




i 


ii 








_„,„,,,, 










„.- — — - 










7SF 


^ 


1A 










ZJ 








1' 




MM 


M 


M 







plan of coffer-dam and system of bracing' 
Fig. 4. 



Plate XIV. 




ELEVAT10.N OF OCTAGONAL CAISSON 

Scale g\o 8 feet. 



Timber in Caisson 
841,389 Ft.B.M. 



INGITUDINAL SECTION, SHOWING INTERIOR DETAILS, SHAFTS, PlPES, IN POSITION. 



Plate XIV. 




Fig. i. Part Elevation, Part Longitudinal Section, showing Interior Details, Shafts, Pipes, in Position. 



Plate XV. 
etails of Construction, Octagonal Caisson. 




quantities: 

Square Timber 217,845.35 Ft. B. M. Concrete 707.23 Cub. Yds. 

Plank 20,462.73 " " " Excavation 116,084.96 Cub. FeeO 

Total Iron 58,618 lbs. 

DIAGRAM SHOWING DISTRIBUTION OF SCREW BOLTS 
AND DRIFT BOLTS IN VERTICALS OF OCTAGONAL AND 
_ RECTANGULAR CAISSONS. 

2 Screw Bolts 41 ins. 3 Screw Bolts 41 ins. 



Scale o£ Feet 



Plate XV. 
Details of Construction, Octagonal Caisson. 



quantities: 

Square Timber 217,845.35 Ft. B. M. Concrete 707.93 Cub. Yds. 



DIAGRAM SHOWING DISTRIBUTION OF SCREW BOLTS 
AND DRIFT BOLTS IN VERTICALS OF OCTAGONAL AND 
._ RECTANGULAR CAISSONS. 

2 Screw Bolts 41 ins. 3 Screw Bolls 41 ins. 




Plate XVI. 

Square Caisson for Masonry Abutment. 




Fig. 2. — Longitudinal Section. 



Plate XVI. 

Square Caisson for Masonry Abutment. 









Fi 


G. 3. 








/ 12X12" 


lis 


\H 1 1 11 


*3 




12x12" 


T3(f 


T 




12x12 




















— r 












Long 


tudinal 


12x12" S» 






[ 


|i 


H 1 1 


& 




so 




12x12 


SS 




L_ 






I" |*4-p 


« r 


I""k)1 





1 1 ! 1 1 1 : 1 1 i 1 1 1 1 1 1 1 1 ¥m 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 



1,1,1 I I, I I 1,1,1 I 1,1 i M.IHiTO 1,1 ; I, 1,1 I, M I I, NTT 1 " 
n Esx 12 ^ 



41 out to out 
s'x 1 » 9' : 



j3xlx9 
=5 Screw Bolt 
j26"out to out 




Fig. i.— Cross-section. 



Fig. 



"ROCK 

-Longitudinal Section. 



Plate XVII. 

:tagonal Caisson for Pivot Pier, Schuykill River Bridge, 
>. Ry. Showing Details of Construction. 

Fig. i. 




Horizontal Sections Octagonal Caisson for Pivot Pier, Schuykill River Bridge, 
B. & O. Rv. Showing Details of Construction. 




Plate XVIII. 
Designs Pneumatic Caissons. 

and Cairo Bridges. Open Crib-work built to any desired Height. 
Fig. 2. 



3, i & 5 show general 
Caissons with 
alls and cutting edge, 
i crib above; air locks 

often used, 
by G.S. MORRISON, 
Chief Engineer 



Fig-. 4. 




CROSS SECTION 

PNEUMATIC CAISSON 

PLATTSMOUTH'S BRIDGE 



Plate XVIII. 
General Designs Pneumatic Caissons. 
Figs, i, 2, 3 and 4 used in Foundations Bismarck and Cairo Bridges. Open Crib-work built to any desired Height. 

Fig. 2. 



Fig. 1. 

-■a 1 — £. ! &_ 



Fig. 4. 




TOP VIEW 4 HORIZONTAL SECTION. 



AtfD 



Csij 



io, Lower Part of Masonry Pier, with Cutwater 




Plate XIX. 
Design of Pneumatic Caisson and Crib with Pointed End; also, Lower Part of Masonry Pier, with Cutwater 




Plate XX. 

ck, Shaft, Pipes, and Details. 



Fig. 3. 




Fig. 4- 




Fig. 7. 



Fig. 6. 



Fig. 5. 




iew of Air- 
haft. 



Figs. 3, 4, and 5. 
Details of Doors, 



Fig. 7. — 
Dischargk-pipb. 



Fig. 6. 

Supply-shaft. 



Plate XX. 
Air-lock, Shaft, Pipes, and Details. 

Fig. 2. 



Fig. 6. 




Fig, i. — Vertical Section through Fig. 2.— Outside View of Air- Figs. 3, 4, and 5. 

Air-lock and Main Shaft. lock and Shaft. Details of Doors. 



Fig. 7. — 
Discharge-pipe. 



Fig. 6. 
Supply-shaft. 



Plate XXI. 
rew-pile Pier, Mobile River, L. & N. Ry. 




Plate XXI. 
Screw-iilb Pier, Mobile River, L. & N. Rv. 
Fir,. I. 




Plate XXII. 
ly Progress Sinking Octagonal Caisson. 

August. Weight 452,250 Lbs. , 



.u.uiiiuni.uim? 1 1 1 i 1 1 1 1 liiumuu 




Plate XXII. 
Daily Progress Sinking Octagonal Caisson. 

Caisson LaniKnol 31s l., August. Weight 452,550 Lus. , 



uiwiiimijujiiiifi 1 1 1 1 1, lauuuiu 

T7TT7TTT" '" i'Vi ii i'T""7 r TT??T7?"TTT7TTT' T 




